Remove memory leak from storing completed tasks

To ensure that we don't end up with lots of "this task was deleted but never ran" warnings we hold onto the tasks
we end up creating and ensure they are cancelled and ran in the loop before they are garbage collected.

Prior to this we were doing that activity at the end of the run, which leads to large memory usage in large test suites

This change makes it so that we perform this garbage collection as we proceed with the tests so that memory can be
released during the run of the test suite

Author: Brian Maissy

alt_pytest_asyncio/converter.py

@@ -21,6 +21,33 @@ def __init__(self) -> None:
             defaultdict(list)
         )
 
+    def _cleanup_completed_tasks(self) -> None:
+        """
+        Remove references to completed tasks to they can be garbage collected, including the
+        return (or yielded) values of the fixture functions, which would otherwise leak memory.
+        """
+        for loop, tasks in list(self._test_tasks.items()):
+            if loop.is_closed():
+                continue
+
+            remaining: list[asyncio.Task[object]] = []
+            finished: list[asyncio.Task[object]] = []
+            for t in tasks:
+                if not t.done():
+                    remaining.append(t)
+                else:
+                    t.cancel()
+                    finished.append(t)
+
+            self._test_tasks[loop] = remaining
+
+            if finished:
+                loop.run_until_complete(asyncio.tasks.gather(*finished, return_exceptions=True))
+
+    def _add_new_task(self, loop: asyncio.AbstractEventLoop, task: asyncio.Task[object]) -> None:
+        self._cleanup_completed_tasks()
+        self._test_tasks[loop].append(task)
+
     def sessionfinish(self) -> None:
         for loop, tasks in self._test_tasks.items():
             ts = []
@@ -227,7 +254,7 @@ def silent_done_task(res: asyncio.Future[protocols.T_Ret | None] | None) -> None
             self._async_runner(async_timeout, func, args, kwargs), context=self._ctx
         )
         task.add_done_callback(silent_done_task)
-        self._test_tasks[loop].append(task)
+        self._add_new_task(loop, task)
 
         return loop.run_until_complete(task)