Enhance MTProxy checker by introducing a new -probe mode deep-strict for stricter response validation. Update README and Docker documentation to clarify probing modes, exit codes, and the new MTPROXY_TDLIB_HELPER and MTPROXY_TDLIB_TIMEOUT environment variables for external helper integration. Refactor connection handling and error reporting to improve robustness and clarity in response verification.

cmd/tdlib_ping/stub.go

@@ -0,0 +1,19 @@
+//go:build !tdlib || !cgo
+
+package main
+
+import (
+	"encoding/json"
+	"os"
+)
+
+func main() {
+	enc := json.NewEncoder(os.Stdout)
+	enc.SetEscapeHTML(false)
+	_ = enc.Encode(map[string]interface{}{
+		"ok":         false,
+		"error":      "tdlib_ping: build with CGO and -tags=tdlib; requires libtdjson (see cmd/tdlib_ping/README.md)",
+		"exit_code":  2,
+	})
+	os.Exit(2)
+}