Implements ClientTraceInfo with TraceMsgDelivery recording and per-client
echo suppression; fixes AccountGoParityTests namespace ambiguity caused by
the new NATS.Server.Tests.Subscriptions test namespace.
Implements RouteResultCache with fixed-capacity LRU eviction and atomic
generation-based invalidation (Go ref: client.go routeCache, maxResultCacheSize=8192).
Fixes AccountGoParityTests namespace ambiguity introduced by new test file.