cachedb_local: raise event on cache entry expiry

[dondetir]

Summary

Add E_CACHEDB_LOCAL_EXPIRED event support, allowing users to be notified via event_route when cached entries expire.

Usage

event_route[E_CACHEDB_LOCAL_EXPIRED] {
    xlog("expired: $param(key) = $param(value) in $param(collection)\n");
    # safe to access the cache from within this handler
    cache_store("local", "reacted_to_$param(key)", "handled", 60);
}

Event Parameters

Parameter	Description
key	The key of the expired cache entry
value	The value of the expired cache entry
collection	The cache collection name

Implementation Details

• The event is raised during the periodic cleanup timer (cache_clean_period), not during lazy expiry on access
• Events are raised outside the per-bucket hash table lock to prevent deadlocks when the event_route handler accesses the cache — expired entry data is copied to pkg memory before lock release
• Uses the standard EVI (Event Interface) framework following the same pattern as usrloc (E_UL_CONTACT_DELETE) and dialog (E_DLG_STATE_CHANGED)
• evi_probe_event() check avoids parameter setup overhead when no subscribers exist

Testing

• Builds clean, zero warnings in new code
• All 2545 unit tests pass
• Runtime verified: event fires with correct key/value/collection parameters
• Deadlock test: event handler successfully writes back to cache from within event_route — no deadlock

Closes #3735