feat: add LruLockMap peek/pop_lru, expand multi-threaded benchmarks

[SF-Zhou]

• Add peek(): read a value without promoting it in the LRU list (~3x faster than get() in a 4-thread read benchmark, since no move_to_front write happens under the shard lock)
• Add pop_lru(): remove and return a least-recently-used entry; per-shard LRU order with round-robin shard selection, in-use entries are skipped like the eviction policy
• Extract key/value ownership on pop via AliasableBox::into_unique
• Add 8 tests covering peek promotion semantics, pop_lru ordering, in-use/empty entry skipping, multi-shard draining and concurrency
• Rewrite benches: concurrent get, mixed get/insert, hot-key entry contention, LRU get vs peek, and mixed workload under eviction pressure, each at 1/4/8 threads with throughput reporting

[Copilot]

Pull request overview

This PR extends LruLockMap with two new LRU-oriented operations—peek (read without LRU promotion) and pop_lru (explicitly remove an LRU entry)—and updates tests, docs, and benchmarks to cover and measure the new behavior.

Changes:

• Add LruLockMap::peek to read values without promoting entries in the shard LRU list.
• Add LruLockMap::pop_lru to remove and return a per-shard LRU entry with round-robin shard selection.
• Expand tests/documentation and rewrite Criterion benchmarks to include multi-threaded workloads and get vs peek comparisons.

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	Implements peek/pop_lru and adds test coverage for semantics and concurrency.
src/lib.rs	Documents the new LRU inspection/removal APIs in crate-level docs.
README.md	Updates the public README with peek/pop_lru feature notes and examples.
CHANGELOG.md	Records the new APIs and benchmark expansion in the changelog.
benches/bench_lockmap.rs	Reworks benches to include multi-threaded workloads and LRU get vs peek.

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[codecov]

Codecov Report

❌ Patch coverage is 98.68421% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.89%. Comparing base (97bfc9d) to head (82ba25c).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lru_lockmap.rs	98.68%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              main      #39      +/-   ##
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- Coverage   100.00%   99.89%   -0.11%     
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  Files            3        3              
  Lines         1812     1964     +152     
===========================================
+ Hits          1812     1962     +150     
- Misses           0        2       +2     

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