fix: fix session managment with retire (apify#947)

### Description

- Fix cases where a session was not excluded from the pool after calling
`session.retire()` inside a successful `request_handler`.

src/crawlee/crawlers/_basic/_basic_crawler.py

@@ -1029,7 +1029,7 @@ async def __run_task_function(self) -> None:
 
             request.state = RequestState.DONE
 
-            if context.session:
+            if context.session and context.session.is_usable:
                 context.session.mark_good()
 
             self._statistics.record_request_processing_finish(statistics_id)

tests/unit/crawlers/_basic/test_basic_crawler.py

@@ -25,6 +25,7 @@
 from crawlee.errors import SessionError, UserDefinedErrorHandlerError
 from crawlee.events._local_event_manager import LocalEventManager
 from crawlee.request_loaders import RequestList, RequestManagerTandem
+from crawlee.sessions import SessionPool
 from crawlee.statistics import FinalStatistics
 from crawlee.storage_clients import MemoryStorageClient
 from crawlee.storage_clients._memory import DatasetClient
@@ -1169,3 +1170,32 @@ async def handler(context: BasicCrawlingContext) -> None:
     await asyncio.gather(crawler_run_task, add_request_task)
 
     mocked_handler.assert_has_calls(expected_handler_calls)
+
+
+@pytest.mark.parametrize(
+    ('retire'),
+    [
+        pytest.param(False, id='without retire'),
+        pytest.param(True, id='with retire'),
+    ],
+)
+async def test_session_retire_in_user_handler(*, retire: bool) -> None:
+    crawler = BasicCrawler(session_pool=SessionPool(max_pool_size=1))
+    sessions = list[str]()
+
+    @crawler.router.default_handler
+    async def handler(context: BasicCrawlingContext) -> None:
+        if context.session:
+            sessions.append(context.session.id)
+
+            context.session.retire() if retire else None
+
+        await context.add_requests(['http://b.com/'])
+
+    await crawler.run(['http://a.com/'])
+
+    # The session should differ if `retire` was called and match otherwise since pool size == 1
+    if retire:
+        assert sessions[1] != sessions[0]
+    else:
+        assert sessions[1] == sessions[0]