Align rusqlite feature passthroughs with 0.40 defaults

[ryanfowler]

Summary

• Disable rusqlite default features at the dependency edge and model async-sqlite defaults explicitly.
• Add pass-through support for the missing public rusqlite features: collation, column_metadata, i128_blob, jiff, preupdate_hook, serialize, and series.
• Update crate docs and agent guidance to reflect the explicit default feature set.

Testing

• cargo check
• cargo check --no-default-features
• cargo check --no-default-features --features "bundled collation column_metadata i128_blob jiff preupdate_hook serialize series"
• cargo test