fix: treat connection refused as transient across all DNS protocols

DoH, DoH3, and DoQ would exit immediately when a service was unavailable,
making them behave differently from regular UDP DNS. This was inconsistent
and prevented using dnsping as a monitoring tool for intermittent service
availability.

Now all protocols continue pinging when connection is refused, showing
"Connection refused" messages and collecting packet loss statistics. Makes
behavior uniform whether you're pinging over UDP, TCP, TLS, QUIC, or HTTP.

Author: farrokhi

dnsping.py

@@ -449,7 +449,9 @@ def main() -> None:
                     except dns.query.NoDOH:
                         die("ERROR: python httpx module not available")
                     except httpx.ConnectError:
-                        die(f"DoH connection failed on port {dst_port}")
+                        if not quiet:
+                            print("Connection refused", flush=True)
+                        continue
                 else:
                     unsupported_feature("DNS-over-HTTPS (DoH)")
 
@@ -465,7 +467,9 @@ def main() -> None:
                                                   source=src_ip, source_port=src_port,
                                                   http_version=dns.query.HTTPVersion.H3)
                     except ConnectionRefusedError:
-                        die(f"DoH3 connection refused on port {dst_port}")
+                        if not quiet:
+                            print("Connection refused", flush=True)
+                        continue
                 else:
                     unsupported_feature("DNS-over-HTTPS/3 (DoH3)")
 
@@ -482,7 +486,9 @@ def main() -> None:
                             print("Request timeout", flush=True)
                         continue
                     except ConnectionRefusedError:
-                        die(f"DoQ connection refused on port {dst_port}")
+                        if not quiet:
+                            print("Connection refused", flush=True)
+                        continue
                     except Exception as e:
                         # Catch QUIC-specific exceptions like UnexpectedEOF
                         if e.__class__.__name__ == 'UnexpectedEOF':