feat(transport): Add kill method for async transport

Implement a kill method that properly shuts down the async transport. The httpcore async connection pool needs
to be explicitly shutdown at the end of its usage.

GH-4582

Author: srothh

sentry_sdk/transport.py

@@ -761,6 +761,16 @@ def _make_pool(
 
         return httpcore.AsyncConnectionPool(**opts)
 
+    def kill(self: Self) -> None:
+
+        logger.debug("Killing HTTP transport")
+        self._worker.kill()
+        for task in self.background_tasks:
+            task.cancel()
+        self.background_tasks.clear()
+
+        self._loop.create_task(self._pool.aclose())  # type: ignore
+
 
 class HttpTransport(BaseHttpTransport):
     if TYPE_CHECKING: