feat(cache): add cache eviction and concurrency tests

[KingingWang]

Summary

• Add as_any() method to Cache trait for downcasting in tests
• Add comprehensive cache eviction tests (TTL expiration, capacity-based)
• Add concurrent access tests (reads, writes, mixed operations, race conditions)

Changes

• src/cache/mod.rs: Add as_any() to Cache trait
• src/cache/memory.rs: Implement as_any() for MemoryCache
• src/cache/redis.rs: Implement as_any() for RedisCache
• tests/unit/cache_tests.rs: Add 7 new tests covering:
  • TTL expiration behavior
  • Capacity-based eviction under pressure
  • Independent TTLs for different cache types
  • 100 concurrent reads
  • 50 concurrent writes
  • 90 mixed concurrent operations
  • Race condition read-after-write

Test plan

• All 24 cache tests pass
• cargo clippy --all-targets -- -D warnings passes
• cargo fmt -- --check passes

[KingingWang]

ProviderModelNotFoundError

opencode session  |  github run

[KingingWang]

ProviderModelNotFoundError

opencode session  |  github run