Always use all selected trains in pulse pattern components

[philsmt]

PulsePattern-based components track train IDs in addition to pulse IDs to handle trains that don't have any pulses, e.g. in methods like pulse_counts(). Unfortunately I noticed only now that all implementations actually only account for trains that have data (in the sense of pulse records, not whether there are actually any pulses). This typically happened by using KeyData.train_id_coordinates() rather than KeyData.train_ids.

This PR fixes this by always using all selected train IDs whether data records exist or not. While I would claim this is the correct behaviour as done in EXtra-data (e.g. KeyData.data_counts()), it is somewhat changing the behaviour. I also had to fix a test to account for this, though it clearly did the wrong thing.

As part of this, I realized all existing implementations of _get_train_ids() can actually be handled by the default implementation in PulsePattern.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.78%. Comparing base (f57e71c) to head (728c621).

Files with missing lines	Patch %	Lines
src/extra/components/pulses.py	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #434      +/-   ##
==========================================
- Coverage   72.83%   72.78%   -0.05%     
==========================================
  Files          35       35              
  Lines        6048     6048              
==========================================
- Hits         4405     4402       -3     
- Misses       1643     1646       +3     

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[JamesWrigley]

LGTM! I have a soft preference for holding off until the next environment (https://github.com/European-XFEL/EXtra/milestone/2) but I'll leave the decision to you.

[philsmt]

Yes, I think that's reasonable. I created a breaking change tag for this (and another PR already waiting for it), so we can locate them quickly.