handle connection close on CancelledError to prevent stale results

[shenchucheng]

Description

This PR resolves an issue where canceled queries using connections from a pool leave unintended results that affect subsequent queries. When a query is canceled, the connection is returned to the pool without proper cleanup, causing future queries to receive residual data from the canceled task.

Solution

• Implemented _close_on_cancel to ensure that connections are fully closed and reset when a query is canceled.
• Added a test case to verify that canceled queries do not impact future connections from the pool.

This update ensures clean connection states on cancellation, improving reliability in pooled query operations. This approach is inspired by similar handling in aiomysql

Related Issues

• Fixes #100
• Fixes #103

[long2ice]

Please run make style ci in local first

[shenchucheng]

Please run make style ci in local first

Okay, I've updated it. Please check again.

[StrayDragon]

Cool, we need this fix, could you please prioritize it? I have to use a forked version now cannot receive update friendly ...