Rename run_with_extra_handlers to run_with_handlers

[congwang-mk]

Aligns the Rust core method names with the FFI and Python API, where the sandlock_run_with_handlers C ABI symbol and Sandbox.run_with_handlers never carried extra.

Renames run_with_extra_handlers / run_interactive_with_extra_handlers (and the internal helper, field, params, tests, and docs). No behavior or ABI change. Rust (561) and Python (321) suites pass.

🤖 Generated with Claude Code

[congwang-mk]

@dzerik Please take a look. Thanks.

[dzerik]

Code review

Clean rename, no blockers. Verified locally against head sha 41d31a4:

• Instrumental grep: for all seven renamed identifiers (run_with_extra_handlers, run_interactive_with_extra_handlers, sandbox_collect_extra_handlers, extra_handlers, extra_handler_tests, test_extra_handlers, ExtraHandler) returns zero matches across crates/, docs/, README.md.
• Build clean: cargo build --release succeeds on the workspace (sandlock-core, sandlock-ffi, sandlock-cli).
• Library tests pass: cargo test --release --lib -p sandlock-core — 275 passed, 0 failed.
• crates/sandlock-ffi/src/handler/run.rs:124-126 correctly call run_interactive_with_handlers / run_with_handlers.
• Doc-comments in dispatch.rs (intra-doc links) and docs/extension-handlers.md are consistent with the new names.
• Trait Handler was already the name; no breaking surface for downstream impl ExtraHandler callers.
• Naming aligns with the C ABI (sandlock_run_with_handlers) and the Python wrapper (Sandbox.run_with_handlers) as the PR description states.