perf: resolve the log channel from the guild cache before fetch_channel

T3-19: _get_channel did an HTTP fetch_channel (GET /channels/{id}) on every
guild-routed log line, in both the self.channel and settings paths. try
guild.get_channel first; fetch only on a cache miss. same channel, same
ValueError normalization.

Signed-off-by: disqualifier <dev@disqualifier.me>

src/dpy_logger/dpy_logger.py

@@ -130,7 +130,10 @@ class DPYLogger:
         raise ValueError("[dpy_logger] no guild available for logging")
 
     async def _get_channel(self, guild, override=False):
-        """resolve the log channel, preferring self.channel when the guild matches"""
+        """resolve the log channel, preferring self.channel when the guild matches
+
+        the guild's channel cache is tried first; fetch_channel (an HTTP GET) only runs on a
+        cache miss (e.g. a fetched, uncached guild)"""
         if not guild:
             raise ValueError("[dpy_logger] cannot resolve channel without a guild")
 
@@ -141,7 +144,7 @@ class DPYLogger:
                 # fetch_channel raises NotFound/Forbidden/HTTPException/InvalidData (a
                 # ClientException, not an HTTPException); normalize all to ValueError
                 try:
-                    channel = await guild.fetch_channel(self.channel)
+                    channel = guild.get_channel(self.channel) or await guild.fetch_channel(self.channel)
                 except (discord.HTTPException, discord.ClientException) as error:
                     raise ValueError(f"[dpy_logger] could not fetch channel {self.channel}: {error}") from error
                 if not isinstance(channel, discord.TextChannel):
@@ -153,7 +156,7 @@ class DPYLogger:
         except KeyError as error:
             raise ValueError(f"[dpy_logger] no log channel configured for guild {guild.id}") from error
         try:
-            channel = await guild.fetch_channel(channel_id)
+            channel = guild.get_channel(channel_id) or await guild.fetch_channel(channel_id)
         except (discord.HTTPException, discord.ClientException) as error:
             raise ValueError(f"[dpy_logger] could not fetch channel {channel_id}: {error}") from error
         if not isinstance(channel, discord.TextChannel):