Module cache 

Tiered LRU cache for Microscope Memory queries.

Two tiers:

• Tier 1 (hot): Exact query → JSON response cache
• Tier 2 (warm): Block index → text cache (avoids repeat mmap reads)

Thread-safe via Mutex. Cache is invalidated on store/rebuild.

Structs

CacheStats

Cache statistics for the /stats endpoint.

QueryCache

Thread-safe two-tier query cache.