Replace bare except with except Exception in task-sdk supervisor

[bramhanandlingala]

Description

Issue #69441 flags exception handlers that catch overly broad types,
which can hide real errors or interfere with signal handling. I looked
for bare except: clauses specifically, since those catch everything
including KeyboardInterrupt/SystemExit. There were two left in the
repo outside of tests/docs.

1. Task-SDK supervisor — the bare except around coordinator init
always re-raised afterward, so signals weren't actually swallowed, just
logged with a misleading traceback before exiting. Narrowed to
except Exception: so real errors are still logged the same way, but
Ctrl+C/shutdown no longer produce that spurious log line.

2. Pytest plugin — a bare except: raise that did nothing (pure
re-raise, no logging). Removed it; the finally below already handles
cleanup.

Didn't touch the other except Exception: blocks in core — those don't
have this bare-except issue, and a full rewrite is a separate effort.

related: #69441

Gen-AI disclosure: I used a generative AI tool to help identify the root
cause, write tests, and draft the PR description. I reviewed, tested, and
verified all changes locally before submitting.

Was generative AI tooling used to co-author this PR?

• Yes — Claude

Generated-by: Claude following the guidelines

[bramhanandlingala]

Hi @Vamsi-klu

Could you please review the code and approve the PR

[shahar1]

See #70437 (review)