fix: Handle exceptions in pre-reboot event listeners via return_exceptions

[vdusek]

Summary

• Add return_exceptions=True to asyncio.gather in Actor.reboot() so a single failing listener no longer prevents others from persisting state
• Log any listener exceptions via self.log.exception

Test plan

• All 182 actor unit tests pass
• Ruff lint clean

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.64%. Comparing base (1610d0d) to head (0d154ca).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@ ## master #843 +/- ## ========================================== + Coverage 86.40% 86.64% +0.23%  ========================================== Files 48 48 Lines 2906 2920 +14 ========================================== + Hits 2511 2530 +19  + Misses 395 390 -5 

Flag	Coverage Δ
e2e	37.87% <0.00%> (-0.19%)	⬇️
integration	59.28% <0.00%> (-0.19%)	⬇️
unit	74.69% <100.00%> (+0.29%)	⬆️

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[Pijukatel]

Could you please add a test to confirm it behaves as expected