refactor: replace ensure_future with create_task

Use the modern asyncio.create_task() in pool.py and server.py.
Replace redundant list comprehension with list() in evict_keys copy.

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

src/s5p/pool.py

@@ -369,8 +369,7 @@ class ProxyPool:
 
         # report evicted proxies to upstream API
         if evict_keys and self._cfg.report_url:
-            dead = [k for k in evict_keys]
-            asyncio.ensure_future(self._report_dead(dead))
+            asyncio.create_task(self._report_dead(list(evict_keys)))
 
     async def _report_dead(self, keys: list[str]) -> None:
         """POST dead proxy list to report_url (fire-and-forget, async)."""

src/s5p/server.py

@@ -292,7 +292,7 @@ async def serve(config: Config) -> None:
         logger.info("reload: config reloaded")
 
     def _on_sighup() -> None:
-        asyncio.ensure_future(_reload())
+        asyncio.create_task(_reload())
 
     loop.add_signal_handler(signal.SIGHUP, _on_sighup)