fix(memory, connection): two data-race/counter defects

1) connection_pool.go: GetConnectionStats read lastRecoveryAttempt (a
multi-word time.Time) without any lock while checkAndRecover wrote it
under recoveryMutex -> data race on live admin API endpoints. Snapshot it
under recoveryMutex (the writer's lock). Regression test
TestGetConnectionStatsRace drives the read path concurrent with the locked
write under -race.

2) cache/memory memory.go: Cache.Get expired path used an unconditional
Delete + atomic decrement, so concurrent Gets on the same expired entry
each decremented entryCount/memoryUsage -> permanent negative drift. Use
LoadAndDelete-with-guard (as evictOldest/evictToFreeMemory already do) so
only the goroutine that actually removes the entry decrements. Regression
test TestMemoryCacheConcurrentGetOnExpiredEntry_CountersConsistent.

connection_pool.go

@@ -259,11 +259,17 @@ func (cpm *ConnectionPoolManager) RecordConnectionFailure() {
 
 // GetConnectionStats returns current connection statistics
 func (cpm *ConnectionPoolManager) GetConnectionStats() map[string]any {
+	// lastRecoveryAttempt is written by checkAndRecover under recoveryMutex
+	// (time.Time is not atomic), so snapshot it under the same lock.
+	cpm.recoveryMutex.Lock()
+	lastRecovery := cpm.lastRecoveryAttempt
+	cpm.recoveryMutex.Unlock()
+
 	return map[string]any{
 		"active_connections":    cpm.activeConnections.Load(),
 		"total_connections":     cpm.totalConnections.Load(),
 		"connection_failures":   cpm.connectionFailures.Load(),
-		"last_recovery_attempt": cpm.lastRecoveryAttempt,
+		"last_recovery_attempt": lastRecovery,
 	}
 }