Enhance MTProxy checker functionality by introducing a new -probe flag for selecting between fast and deep probing modes. Update README and Docker documentation to reflect this change, including details on timeout handling and exit codes for improved clarity.

internal/checkresult/checkresult.go

@@ -16,6 +16,9 @@ func Classify(err error) (exitCode int, message string) {
 	if errors.Is(err, checker.ErrProxyClosed) {
 		return 3, err.Error()
 	}
+	if errors.Is(err, checker.ErrNoDataAfterHeader) {
+		return 1, err.Error()
+	}
 	if errors.Is(err, context.DeadlineExceeded) {
 		return 4, "timeout"
 	}