feat: add LruLockMap batch_lock; dedup State and release protocol into common module

[SF-Zhou]

• Add batch_lock to LruLockMap: deadlock-safe multi-key locking via sorted BTreeSet order; held keys are never evicted (refcnt > 0 is skipped by try_evict), plus an 8-thread concurrent test
• Generalize the per-key State as State<K, V, L> in src/common.rs, where L is an extra link payload: () for LockMap and the intrusive LRU list pointers (Links) for LruLockMap; layout is unchanged (links: () is a ZST, field nesting is compile-time)
• Extract the reference-release CAS fast path into State::release_ref_needs_cleanup(), removing the duplicated protocol from both maps' release_ref
• Verified: 69 unit tests + 44 doctests, clippy -D warnings, full Miri and ThreadSanitizer runs all clean; criterion comparison vs pre-refactor baseline shows no significant regression on any benchmark (several hot paths slightly improved from codegen side effects)

[Copilot]

Pull request overview

This PR extends LruLockMap with deadlock-safe multi-key locking (batch_lock) and refactors shared per-entry bookkeeping into src/common.rs so LockMap and LruLockMap reuse the same State and reference-release fast path.

Changes:

• Add LruLockMap::batch_lock that locks keys in a consistent sorted order via BTreeSet.
• Deduplicate per-entry State (now generic over an extra payload) and the reference-release CAS fast path into src/common.rs.
• Update docs/changelog to reflect the new API and internal refactor.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/lru_lockmap.rs	Introduces batch_lock, moves LRU link pointers into a payload type, and switches to shared State + shared release fast path; adds a concurrency test.
src/lockmap.rs	Switches to the shared State type and shared release_ref_needs_cleanup() fast path.
src/common.rs	Adds the shared State<K,V,L> implementation and extracts the reference-release CAS fast path into release_ref_needs_cleanup().
README.md	Documents batch locking support for LruLockMap.
CHANGELOG.md	Notes the new batch_lock API and internal deduplication work.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.29%. Comparing base (b659cd5) to head (69a9375).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
- Coverage   99.29%   99.29%   -0.01%     
==========================================
  Files           3        3              
  Lines        2277     2272       -5     
==========================================
- Hits         2261     2256       -5     
  Misses         16       16              

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.