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.

internal/tgquick/probe_test.go

@@ -34,3 +34,15 @@ func TestIsResPQ(t *testing.T) {
 		t.Fatal("expected resPQ")
 	}
 }
+
+func TestIsUnencryptedDCEnvelope(t *testing.T) {
+	msgData := make([]byte, 8)
+	binary.LittleEndian.PutUint32(msgData, 0x11223344)
+	w := wrapUnencrypted(msgData)
+	if !isUnencryptedDCEnvelope(w) {
+		t.Fatal("expected envelope for arbitrary constructor")
+	}
+	if isResPQ(w) {
+		t.Fatal("not resPQ")
+	}
+}