[Store] Remove unused LRU eviction strategy

[Aionw]

Description

Remove the unused LRUEvictionStrategy implementation and its dedicated unit tests. The strategy has no production callers; the existing FIFO eviction strategy and its coverage remain unchanged.

This is a code cleanup with no user-facing behavior change.

Module

• Transfer Engine (mooncake-transfer-engine)
• Mooncake Store (mooncake-store)
• Mooncake EP (mooncake-ep)
• Mooncake PG (mooncake-pg)
• Integration (mooncake-integration)
• P2P Store (mooncake-p2p-store)
• Python Wheel (mooncake-wheel)
• Common (mooncake-common)
• Mooncake RL (mooncake-rl)
• CI/CD
• Docs
• Other

Type of Change

• Bug fix
• New feature
• Refactor
• Breaking change
• Documentation update
• Performance improvement
• Other

How Has This Been Tested?

Test commands:

cmake --build build --target eviction_strategy_test --parallel 128
./build/mooncake-store/tests/eviction_strategy_test
pre-commit run --files mooncake-store/include/eviction_strategy.h mooncake-store/tests/eviction_strategy_test.cpp

Test results:

• Unit tests pass
• Integration tests pass (not applicable)
• Manual testing done (not applicable)

Checklist

• I have performed a self-review of my own code
• I have formatted my code using ./scripts/code_format.sh
• I have run pre-commit run --all-files and all hooks pass
• I have updated the documentation (not applicable; no user-facing behavior change)
• I have added tests to prove my changes are effective (not applicable; unused code and its tests were removed)
• For changes >500 LOC: I have filed an RFC issue (not applicable)

The pre-commit hooks pass for all files changed by this PR.

AI Assistance Disclosure

• No AI tools were used
• AI tools were used (specified below)

OpenAI Codex identified references, prepared the cleanup, ran validation, and drafted this PR description. The human submitter is responsible for reviewing and understanding every changed line.