perf(runtime): pool the local xray gRPC connection (#6916)

A client per runtime operation made a bulk delete pay a TCP and HTTP/2
handshake for every client. The local runtime now keeps one gRPC client
per API port and replaces it when a core restart moves the port; the
traffic poll keeps its own client, since StatsLastValues is unlocked.

A pooled channel keeps grpc-go's reconnect backoff after the core
restarts, so a call that fails with Unavailable drops the client and
dials again, as a client per call did.

internal/web/runtime/local_api.go

@@ -0,0 +1,52 @@
+package runtime
+
+import (
+	"sync"
+
+	"github.com/mhsanaei/3x-ui/v3/internal/xray"
+)
+
+// One pooled gRPC client serves local runtime operations; never use it for traffic stats, whose
+// unlocked StatsLastValues a second reader would corrupt, so the traffic poll keeps its own client.
+var (
+	localAPIMu     sync.Mutex
+	localAPIPort   int
+	localAPIClient *xray.XrayAPI
+)
+
+// localAPIForPort returns the pooled client for the API port, replacing (and closing) it when a core
+// restart moved the port; callers must not close it.
+func localAPIForPort(port int) (*xray.XrayAPI, error) {
+	localAPIMu.Lock()
+	defer localAPIMu.Unlock()
+
+	if localAPIClient != nil {
+		if localAPIPort == port {
+			return localAPIClient, nil
+		}
+		localAPIClient.Close()
+		localAPIClient = nil
+	}
+
+	api := &xray.XrayAPI{}
+	if err := api.Init(port); err != nil {
+		return nil, err
+	}
+	localAPIClient = api
+	localAPIPort = port
+	return api, nil
+}
+
+// evictLocalAPIClient closes the pooled client so the next call dials a fresh connection, unless
+// another call already replaced the one that failed.
+func evictLocalAPIClient(api *xray.XrayAPI) {
+	localAPIMu.Lock()
+	defer localAPIMu.Unlock()
+
+	if localAPIClient != api {
+		return
+	}
+	localAPIClient.Close()
+	localAPIClient = nil
+	localAPIPort = 0
+}