SchemaCache core library implementation

[BobbieBarker]

Summary

• Complete SchemaCache implementation with SMKES (Schema Mutation Key Eviction Strategy)
• Read-through, write-through, and eviction-based cache invalidation
• Adapter behaviour with optional init/0 callback and boot-time capability resolution
• KeyRegistry for compact integer ID mapping
• SetLock partitioned lock fallback for adapters without native set ops
• ETS adapter with native set operations