fix(checkpoint): fix AsyncBatchedBaseStore getting stuck

This commit fixes #5503

Gist of it is:

- `asyncio.exception.InvalidStateError` were being raised when the
  future was cancelled
- this exception bubbled up and killed the background task
- `AsyncBatchedBaseStore` stopped doing queries because the background
  task wasn't running anymore

This commit adds some "if future is not done" checks to guard against
this.

libs/checkpoint/langgraph/store/base/batch.py

@@ -343,10 +343,14 @@ async def _run(
 
                     # set the results of each operation
                     for fut, result in zip(futs, results):
-                        fut.set_result(result)
+                        # guard against future being done (e.g. cancelled)
+                        if not fut.done():
+                            fut.set_result(result)
                 except Exception as e:
                     for fut in futs:
-                        fut.set_exception(e)
+                        # guard against future being done (e.g. cancelled)
+                        if not fut.done():
+                            fut.set_exception(e)
             finally:
                 # remove strong ref to store
                 del s