feat: return a cleanup job from drop_function (#4237)

Dropping a Function can leave its content to a server-side cleanup job,
so the name drop and the content deletion become separate events a
caller may want to wait on.

`drop_function_async` returns the unbind result alongside a `Job` for
the cleanup, the same shape `drop_table_async` and
`drop_materialized_view_async` already use: a `202` carries the job id,
and a `200` — an inline deletion, or a name that was not bound — yields
an already-finished job with no id. A `202` without a usable job id is
rejected rather than silently reported as finished.

`drop_function` keeps its `bool` result and now delegates, so nothing
changes for callers that do not care when the content goes.

Available on `Connection` in Rust and on both the sync and asyncio
Python connections.

python/src/connection.rs

@@ -768,6 +768,21 @@ impl Connection {
         })
     }
 
+    pub fn drop_function_async(
+        self_: PyRef<'_, Self>,
+        name: String,
+        version: String,
+    ) -> PyResult<Bound<'_, PyAny>> {
+        let inner = self_.get_inner()?.clone();
+        future_into_py(self_.py(), async move {
+            inner
+                .drop_function_async(name, version)
+                .await
+                .infer_error()
+                .map(|(dropped, job)| (dropped, crate::job::Job::new(job)))
+        })
+    }
+
     #[pyo3(signature = (name, value, namespace_path=None))]
     pub fn create_secret(
         self_: PyRef<'_, Self>,