- Add maxKeys limit (10,000) to NodeCache to prevent unbounded memory growth
- Skip caching undefined values when GeoIP/ASN lookups fail (e.g., when MaxMind DB not configured)
- Add periodic cache statistics logging every 5 minutes for monitoring
- Fixes memory leak where cache would grow indefinitely with high request volumes
The maxKeys limit uses LRU eviction, so oldest entries are automatically removed
when the limit is reached. With ~10k requests/day and 5min TTL, 10k keys provides
ample headroom while preventing OOM issues.
Fixes#2120
