feat: concurrent command dispatch and profiling test client

Replace sequential await in command/event dispatch with
asyncio.create_task() so slow commands (whois, httpcheck, tlscheck)
no longer block the read loop. Add _spawn() for task lifecycle
tracking. Enable cProfile in docker-compose for profiling. Add
scripts/test_client.py for end-to-end plugin testing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/derp/bot.py

@@ -32,6 +32,7 @@ class Bot:
         self.prefix: str = config["bot"]["prefix"]
         self._running = False
         self._started: float = time.monotonic()
+        self._tasks: set[asyncio.Task] = set()
 
     async def start(self) -> None:
         """Connect, register, join channels, and enter the main loop."""
@@ -91,20 +92,17 @@ class Bot:
             await self.conn.send(format_msg("NICK", self.nick))
             return
 
-        # Dispatch to event handlers
+        # Dispatch to event handlers (fire-and-forget)
         event_type = msg.command
         for handler in self.registry.events.get(event_type, []):
-            try:
-                await handler.callback(self, msg)
-            except Exception:
-                log.exception("error in event handler %s", handler.name)
+            self._spawn(handler.callback(self, msg), name=f"event:{handler.name}")
 
         # Dispatch to command handlers (PRIVMSG only)
         if msg.command == "PRIVMSG" and msg.text:
-            await self._dispatch_command(msg)
+            self._dispatch_command(msg)
 
-    async def _dispatch_command(self, msg: Message) -> None:
-        """Check if a PRIVMSG is a bot command and dispatch it."""
+    def _dispatch_command(self, msg: Message) -> None:
+        """Check if a PRIVMSG is a bot command and spawn it."""
         text = msg.text
         if not text or not text.startswith(self.prefix):
             return
@@ -117,14 +115,26 @@ class Bot:
         if handler is _AMBIGUOUS:
             matches = [k for k in self.registry.commands if k.startswith(cmd_name)]
             names = ", ".join(self.prefix + m for m in sorted(matches))
-            await self.reply(msg, f"Ambiguous command '{self.prefix}{cmd_name}': {names}")
+            self._spawn(self.reply(msg, f"Ambiguous command '{self.prefix}{cmd_name}': {names}"),
+                         name=f"cmd:{cmd_name}:ambiguous")
             return
 
+        self._spawn(self._run_command(handler, cmd_name, msg), name=f"cmd:{cmd_name}")
+
+    async def _run_command(self, handler: Handler, cmd_name: str, msg: Message) -> None:
+        """Execute a command handler with error logging."""
         try:
             await handler.callback(self, msg)
         except Exception:
             log.exception("error in command handler '%s'", cmd_name)
 
+    def _spawn(self, coro, *, name: str | None = None) -> asyncio.Task:
+        """Spawn a background task and track it for cleanup."""
+        task = asyncio.create_task(coro, name=name)
+        self._tasks.add(task)
+        task.add_done_callback(self._tasks.discard)
+        return task
+
     def _resolve_command(self, name: str) -> Handler | None:
         """Resolve a command name, supporting unambiguous prefix matching.