feat(utils): ExpiringMapCache + StoreCache (scavenged from openclaw)

[kobie3717]

Two-tier session file caching and generic TTL cache patterns extracted from openclaw/openclaw codebase to replace ad-hoc Map+setTimeout patterns.

ExpiringMapCache:

• Generic TTL cache with automatic expiration
• Background prune sweeps expired entries
• Injectable clock for testing
• Tests: 9 tests covering TTL, pruning, stop(), size()

SessionStoreCache (stores/store-cache.ts):

• Two-tier cache: raw file content + parsed JSON
• Fingerprint-based invalidation (mtime + size)
• LRU eviction at maxEntries (default 100)
• Injectable filesystem adapter for testing
• Tests: 9 tests covering cache hits/misses, LRU, invalidation

Changes:

• Enhanced src/cache/expiring-map.ts (already existed)
• Added src/stores/store-cache.ts (new)
• Added src/tests/store-cache.test.ts (9 tests)
• Enhanced src/tests/expiring-map.test.ts (9 tests)
• Updated package-lock.json (dev dependencies)

All 210 tests pass. No breaking changes to public API.

Description

Brief description of changes.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Checklist

• Tests pass (npm test)
• Types check (npm run typecheck)
• Lint passes (npm run lint)
• Added/updated tests for changes
• Updated documentation if needed
• Follows conventional commit format