Fix mojibake in DX cluster and RBN spot comments

Both providers always decoded telnet bytes as Latin-1, which silently
mangles nodes that send UTF-8 (Latin-1 decode never raises, so mixed
encodings across cluster nodes went unnoticed). Added a shared
decode_telnet_bytes() helper that tries UTF-8 first and falls back to
Latin-1, since a byte stream that happens to be valid multi-byte UTF-8
is essentially never accidental Latin-1 text.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

providers/spot/rbn.py

@@ -9,7 +9,7 @@ import telnetlib3
 
 from core.config import SERVER_OWNER_CALLSIGN
 from data.spot import Spot
-from providers.spot.spot_provider import SpotProvider
+from providers.spot.spot_provider import SpotProvider, decode_telnet_bytes
 
 logger = logging.getLogger(__name__)
 
@@ -81,7 +81,7 @@ class RBN(SpotProvider):
                 try:
                     # Check new telnet info against regular expression
                     telnet_output = self._telnet.read_until("\n".encode("latin-1"))
-                    match = self._LINE_PATTERN.match(telnet_output.decode("latin-1"))
+                    match = self._LINE_PATTERN.match(decode_telnet_bytes(telnet_output))
                     if match:
                         spot_time = datetime.strptime(match.group(5), "%H%MZ").replace(tzinfo=pytz.UTC)
                         spot_datetime = datetime.combine(