emcy: catch callback exceptions and expand test coverage

[friederschueler]

What type of PR is this?

/kind bugfix test
/area emcy.py

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What this PR does / why we need it

This PR incorporates the review feedback from #604 (by @yuvraj-kolkar17) as suggested by @acolomb, since the original contributor has been unresponsive for several months.

Bug fix in canopen/emcy.py:
An exception raised in one EMCY callback would silently abort all subsequent callbacks in the list. The on_emcy() loop now wraps each callback in try/except and logs the exception, so remaining callbacks are always called.

Test improvements in test/test_emcy.py:

• Convert leading comment to docstring in test_emcy_consumer_on_emcy
• Remove superfluous inline # Dispatch … comments
• test_emcy_consumer_initialization: verify initial state (without testing threading.Condition type as an implementation detail)
• test_emcy_consumer_multiple_callbacks: simplified using lambdas
• test_emcy_consumer_callback_exception_handling: rewritten with lambdas; adds assertion assertEqual(['success1', 'success2']) that verifies the fix
• test_emcy_consumer_error_reset_variants: various reset code patterns
• test_emcy_consumer_wait_timeout_edge_cases: zero/near-zero timeouts
• test_emcy_consumer_wait_concurrent_errors: multiple concurrent errors
• TestEmcyIntegration: producer-consumer roundtrip tests using network.subscribe() instead of manual rxbus.recv() calls
• Removed tests that only exercised internal implementation details or Python's own exception mechanism

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Which issue(s) this PR fixes

Closes #604

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Does this PR introduce a user-facing change?

NONE

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[acolomb]

It would really help the review process if you based your version on top of the commits in #604. Is that feasible? It will be squashed anyway when merging.

[friederschueler]

I really tried to rebase this commit to #604 and then apply the changes, but even with AI this didn't work.

Instead here is a summary of how #659 addresses your specific review comments on #604:

Your review comment on #604	Addressed in #659
Convert comment to docstring	✅ Done
Superfluous # Dispatch … comments	✅ Removed
emcy_received type is an implementation detail	✅ Removed
Simplify callbacks with lambdas	✅ Done
len(callbacks) is not public API	✅ Removed
successful_callbacks unused — check actual behavior	✅ assertEqual(['success1', 'success2'])
"Avoid artificial delays" (time_expiry_during_execution)	✅ Removed
Human-readable string checks are fragile	✅ Only assertIn(f"0x{code:04X}", s)
Why not use network.subscribe()?	✅ Integration tests use rx_net.subscribe()
Redundant tests (struct_packing, network_assignment, emcy_error_inheritance)	✅ Removed

Additionally, #659 includes the actual bug fix in emcy.py (try/except around each callback) which #604 does not.