[electrum] fix flaky tear-down in functional tests

Summary:
When the `daemon stop` command in called in the `fulcrum_service`'s tear-down, it returns before all the the threads are terminated. In particular the wallet files still need to be saved before the daemon process exits. This causes a race condition when the test fixture deletes the data directory while `WalletStorage._write` creates a tmp file then deletes it. See python/cpython#14064 for a description of how `shutil.rmtree` ends up raising a `FileNotFoundError`.

This issue will go away in Python 3.13 when `shutil.rmtree` no longer fails because it failed to delete an already deleted file. In the meantime ignore these failures.

I first tried a different approach: wait for the daemon process to actually terminate before deleting the data. However detecting the correct deamon process is not trivial, and if done wrong could cause more flakiness.

Test Plan: `pytest electrumabc/tests/regtest`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15989

Author: PiRK

electrum/electrumabc/tests/regtest/util.py

@@ -1,3 +1,4 @@
+import contextlib
 import os
 import platform
 import shutil
@@ -225,7 +226,12 @@ def fulcrum_service(docker_services: Any) -> Generator[None, None, None]:
         yield
         stop_ec_daemon(electrum_datadir)
     finally:
-        shutil.rmtree(electrum_datadir)
+        # Remove the data directory, ignore race conditions caused by tmp wallet files
+        # created and deleted in WalletStorage._write while the daemon process is
+        # stopping
+        # See https://github.com/python/cpython/pull/14064
+        with contextlib.suppress(FileNotFoundError):
+            shutil.rmtree(electrum_datadir)
 
 
 def wait_for_len(json_req, expected_len: int, timeout=DEFAULT_TIMEOUT):