feat: retain raw BGP attributes, add AIGP/BFD/Prefix-SID/BIER/SFP parsers

[digizeph]

Summary

BGP path attributes that bgpkit-parser does not semantically decode are no longer silently dropped. The parser now distinguishes three undecoded buckets and preserves all original bytes for faithful re-encoding:

• Raw: Known, assigned attribute codes whose value format is not yet parsed. These are preserved verbatim for inspection and round-trip.
• Deprecated: Historic or deprecated code points per IANA. Preserved for archival fidelity and auditing.
• Unknown: Unassigned or unrecognized code points. Preserved so that no wire data is ever lost.

Breaking changes

All breaking changes affect advanced attribute-level usage only:

• AttrRaw fields changed: attr_type: AttrType to code: u8, bytes: Vec<u8> to Bytes. Use .attr_type() to recover the enum.
• AttrType::CLUSTER_ID = 13 removed. Code 13 is the deprecated RCID_PATH / CLUSTER_ID per IANA registry; handled as Deprecated(AttrRaw).
• AttributeValue gains variants: Raw(AttrRaw), BfdDiscriminator, BgpPrefixSid, Bier, Sfp.
• AigpTlv.value: Vec<u8> to Bytes.

No changes to the common iteration/element APIs (into_elem_iter(), MrtElem / BgpElem fields, into_update_iter()). Raw-retained attributes are surfaced through the existing elem.unknown field.

New features

• Raw retention: Known but undecoded codes (0, 22, 24, 27, 33, 128) retained as AttributeValue::Raw instead of dropped.
• Deprecated handling: Removed CLUSTER_ID from AttrType; deprecated codes detected via helper before enum dispatch.
• BIER code 41 (RFC 9793): Added to AttrType per IANA.
• Typed parser failure fallback: Malformed known attributes retain original bytes as Raw after recording a validation warning.
• Serialization: serde enabled on bytes to serialize AttrRaw.

New attribute parsers

RFC	Code	Attribute	What it does
RFC 7311	26	AIGP	Parses TLVs, preserves unknown, round-trip
RFC 9015	37	SFP	Parses 1+2 TLVs, preserves unknown, round-trip
RFC 9026	38	BFD Discriminator	Parses mode + discriminator + optional TLVs, round-trip
RFC 8669	40	BGP Prefix-SID	Parses 1+2 TLVs, preserves unknown, round-trip
RFC 9793	41	BIER	Parses 2+2 TLVs, preserves unknown, round-trip

Examples

• examples/raw_attributes.rs -- API walkthrough for all attribute categories
• examples/scan_path_attributes.rs -- scan RouteViews/RIS archives for rare attributes

What is intentionally raw-retained (deferred)

• Traffic Engineering (code 24) -- tracked in #290
• RTR v2 ASPA PDU support -- tracked in #289
• PMSI_TUNNEL (22, 27), BGPsec_PATH (33), ATTR_SET (128) -- raw-retained

Test coverage

• 641 tests pass (all features), including targeted tests for:
  • raw retention round-trip for all covered codes
  • deprecated code 13 handling
  • unassigned code to Unknown
  • malformed typed parser to warning + Raw retention
  • all 5 new TLV parsers (valid parse, empty, truncation, unknown TLV, round-trip)
• cargo clippy --all-targets --all-features -- -D warnings clean
• cargo llvm-cov shows >90% line coverage across all new parser files

[codecov]

Codecov Report

❌ Patch coverage is 96.52605% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.93%. Comparing base (d9889d1) to head (a29f9bf).

Files with missing lines	Patch %	Lines
src/parser/bgp/attributes/attr_26_aigp.rs	96.55%	3 Missing ⚠️
src/parser/bgp/attributes/attr_37_sfp.rs	95.31%	3 Missing ⚠️
...rc/parser/bgp/attributes/attr_40_bgp_prefix_sid.rs	95.52%	3 Missing ⚠️
src/parser/bgp/attributes/attr_41_bier.rs	95.45%	3 Missing ⚠️
...parser/bgp/attributes/attr_38_bfd_discriminator.rs	97.56%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #291      +/-   ##
==========================================
+ Coverage   89.69%   89.93%   +0.24%     
==========================================
  Files          86       91       +5     
  Lines       18334    18733     +399     
==========================================
+ Hits        16444    16848     +404     
+ Misses       1890     1885       -5     

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[Copilot]

Pull request overview

This PR extends bgpkit-parser’s BGP UPDATE path-attribute handling to (1) preserve undecoded attribute bytes for faithful round-trip encoding and (2) add typed TLV parsers/encoders for several RFC-defined attributes (AIGP, SFP, BFD Discriminator, Prefix-SID, BIER). It also updates the public models/API to carry raw bytes via bytes::Bytes and documents the breaking changes.

Changes:

• Preserve attribute value bytes for known-but-unsupported codes (AttributeValue::Raw), deprecated codes (Deprecated), and unassigned/unknown codes (Unknown), with typed-parser failure fallback to Raw.
• Add parsers/encoders for AIGP (26), SFP (37), BFD Discriminator (38), BGP Prefix-SID (40), and BIER (41), plus supporting model types (RawTlv*, new AttributeValue variants).
• Update docs/examples/changelog and dependency features (enable bytes/serde, make bytes non-optional).

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/parser/mrt/mrt_elem.rs	Updates MRT-to-BgpElem extraction to recognize new attribute variants (but currently drops Raw at this layer).
src/parser/bgp/attributes/README.md	Refreshes attribute support matrix and limitations to reflect typed parsers + raw-retention behavior.
src/parser/bgp/attributes/mod.rs	Implements raw/deprecated/unknown retention in attribute parsing and adds dispatch/encoding for new typed attributes.
src/parser/bgp/attributes/attr_26_aigp.rs	New AIGP TLV parser/encoder with round-trip tests.
src/parser/bgp/attributes/attr_37_sfp.rs	New SFP TLV parser/encoder with round-trip tests.
src/parser/bgp/attributes/attr_38_bfd_discriminator.rs	New BFD Discriminator parser/encoder (mode + discriminator + optional TLVs) with tests.
src/parser/bgp/attributes/attr_40_bgp_prefix_sid.rs	New BGP Prefix-SID TLV parser/encoder with tests.
src/parser/bgp/attributes/attr_41_bier.rs	New BIER TLV parser/encoder with tests.
src/models/network/mpls.rs	Adds an allow(unused_imports) workaround for feature-gated imports (can be made more precise).
src/models/bgp/attributes/mod.rs	Updates attribute models for Bytes, adds new attribute variants + raw TLV helpers, removes CLUSTER_ID, adds BIER.
src/lib.rs	Documents newly supported typed BGP path attributes and raw retention behavior.
README.md	Mirrors crate-level documentation updates for new typed attributes and raw retention.
examples/scan_path_attributes.rs	New example to scan MRT archives for deprecated/unknown/raw-retained attributes.
examples/raw_attributes.rs	New example demonstrating inspecting/round-tripping raw/deprecated/unknown attributes.
CHANGELOG.md	Adds an Unreleased entry documenting breaking changes, new features, and new parsers.
Cargo.toml	Makes bytes non-optional and enables bytes/serde under the crate’s serde feature.

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