Segmentation fault on 0.31.0 when inside a Temporal activity

@fantix is already working on this.

Since Dec 6, 2025.

I'm not sure if the root cause is with `asyncpg` or with `temporal` but this code works fine on `0.30.0`, and crashes on `0.31.0` in `await asyncpg.connect`. Python 3.12.9.

```py
#!/usr/bin/env python
import asyncio
import threading
from datetime import datetime, timedelta

import asyncpg
from temporalio import activity, workflow
from temporalio.client import Client
from temporalio.worker import Worker

TASK_QUEUE = "asyncpg-temporal-test"

async def db_call(label: str) -> None:
"""Connect to Postgres and close."""
loop = asyncio.get_running_loop()
print(f"[{label}] thread={threading.get_ident()} loop_id={id(loop)} {loop!r}")

conn = await asyncpg.connect(
host="localhost",
port=5432,
database="database",
user="andrei",
)

print(f"[{label}] connected to Postgres")

await conn.close()

@activity.defn
async def db_activity() -> None:
return await db_call("activity")

@workflow.defn
class TestWorkflow:
@workflow.run
async def run(self) -> None:
print("[workflow] starting db_activity")
return await workflow.execute_activity(
db_activity,
start_to_close_timeout=timedelta(seconds=30),
task_queue=TASK_QUEUE,
)

async def main() -> None:
# 1) Baseline: asyncpg on a fresh loop, no Temporal
print("=== 1) Direct asyncpg on fresh loop (no Temporal) ===")
await db_call("direct")

# 2) Bring up Temporal client + worker and run a workflow that calls db_activity
print("\n=== 2) Temporal worker + workflow calling async activity ===")
client = await Client.connect("localhost:7233")
worker = Worker(
client,
task_queue=TASK_QUEUE,
workflows=[TestWorkflow],
activities=[db_activity],
)

async with worker:
# This executes TestWorkflow.run, which in turn executes db_activity
result = await client.execute_workflow(
TestWorkflow.run,
id=datetime.now().isoformat(),
task_queue=TASK_QUEUE,
)
print(f"[main] workflow result: {result}")

if __name__ == "__main__":
asyncio.run(main())
```

Repro steps:

1. Start a temporal server: `temporal server start-dev`
2. In a separate terminal, run the code above:
```sh
% python test_asyncpg.py

=== 1) Direct asyncpg on fresh loop (no Temporal) ===
[direct] thread=8654430720 loop_id=4353195520 <_UnixSelectorEventLoop running=True closed=False debug=False>
[direct] connected to Postgres

=== 2) Temporal worker + workflow calling async activity ===
[workflow] starting db_activity
[activity] thread=8654430720 loop_id=4353195520 <_UnixSelectorEventLoop running=True closed=False debug=False>
zsh: segmentation fault python test_asyncpg.py
```