AsyncConnection: a cancelled execute() returns None instead of raising #59

This work was produced with the help of language models.

AsyncConnection.execute() catches asyncio.CancelledError, interrupts the connection and returns None. A cancelled task therefore looks like a normal return: task.cancelled() is false, loops keep running after cancellation, and asyncio.wait_for() / asyncio.timeout() return None instead of raising TimeoutError.

In the same code path:

• Cancelling a task that is still waiting for a free connection interrupts whatever query runs on that connection, i.e. another task's query.
• The connection counter is released when the awaiting task exits, while the query may still be running.
• execute() with a PreparedStatement from a connection outside the pool raises UnboundLocalError.

import asyncio, ladybug as lb

async def main():
    ac = lb.AsyncConnection(lb.Database(":memory:"))
    q = "WITH range(1, 30000) AS r UNWIND r AS x UNWIND r AS y RETURN sum(x * y)"
    print(await asyncio.wait_for(ac.execute(q), 0.5))

asyncio.run(main())

Expected: asyncio.TimeoutError after 0.5 s.
Actual: prints None.

Reproduced with the ladybug==0.21.2 wheel on CPython 3.13.16 and 3.14.8, and on main (548c183) with CPython 3.12.

Fix: #64