fix: prevent task GC in AsyncTeleBot by tracking background tasks

[gilangjavier]

This fix addresses the issue where was called without storing a strong reference to the task, leading to potential premature garbage collection. We now maintain a set of background tasks and add a done callback to discard them upon completion.Fixes #2572

[gilangjavier]

I checked this PR and currently no CI checks are being reported on the branch (gh pr checks returns none), so status stays UNSTABLE.

Could a maintainer confirm how CI should be triggered for external contributor PRs in this repo? If there is a label/command/manual trigger needed, I can follow it.

[Badiboy]

Triggered.

[Copilot]

Pull request overview

This PR fixes a potential asyncio garbage-collection issue in AsyncTeleBot polling by retaining strong references to “fire-and-forget” tasks created for update processing, aligning with Python’s asyncio.create_task() guidance.

Changes:

• Add an instance-level _background_tasks set to retain created asyncio.Task objects.
• Track each process_new_updates() task and discard it from the set when it completes.

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[gilangjavier]

Follow-up with exact fixes for Copilot feedback:

• Added explicit typing for background task tracking: _background_tasks: set[asyncio.Task[Any]].
• Replaced the discard-only callback with _on_background_task_done + _process_background_task_result so task exceptions are always retrieved and routed through _handle_exception/logger (prevents "Task exception was never retrieved").
• Added _shutdown_background_tasks() and call it in polling finally before close_session(): wait briefly for in-flight update tasks, then cancel/drain remaining tasks before closing aiohttp session.

Commit: a01eda6

Please re-review when convenient 🙏