fix(ecstore): replace unbounded metadata cache with moka
Replace the manual Arc<RwLock<HashMap>> metadata cache with
moka::future::Cache, which provides:
- Built-in LRU eviction when max_capacity is reached
- Automatic TTL expiry via time_to_live (250ms)
- Lock-free concurrent reads
- Non-blocking invalidation
Fixes the memory leak risk from unbounded HashMap and the
all-or-nothing eviction logic that cleared all entries at once.
Closes#743
Co-authored-by: houseme <[email protected]>
