fix(core): Gracefully handle invalid date format in preferences

[sentry]

This PR addresses issue NURSE-SCHEDULING-1W where an invalid date string, such as 'Freeday_' (a typo of a date group ID), provided in a preference would cause a ValueError in _parse_single_date.

Previously, this ValueError propagated unhandled through scheduler.schedule to OptimizationRunner.run, leading to an unexpected job crash.

The fix involves wrapping the scheduler.schedule call within OptimizationRunner.run in core/nurse_scheduling/server/jobs/runner.py with a try/except ValueError block. If a ValueError occurs during scheduling, it is now caught, and a JobFailure with code="invalid_model" and the original error message is returned. This ensures that the optimization job fails gracefully with a clear, user-facing error message instead of crashing.

Fixes NURSE-SCHEDULING-1W

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.63%. Comparing base (246cb4d) to head (48595b9).

Files with missing lines	Patch %	Lines
core/nurse_scheduling/server/jobs/runner.py	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #51      +/-   ##
==========================================
- Coverage   92.65%   92.63%   -0.03%     
==========================================
  Files         100      100              
  Lines        8250     8253       +3     
  Branches      705      705              
==========================================
+ Hits         7644     7645       +1     
- Misses        460      462       +2     
  Partials      146      146              

Flag	Coverage Δ
core	94.12% <50.00%> (-0.04%)	⬇️
core-macos	?
core-windows	94.12% <50.00%> (-0.04%)	⬇️
web-frontend	88.84% <ø> (ø)
web-frontend-macos	88.84% <ø> (ø)
web-frontend-windows	88.84% <ø> (ø)

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Files with missing lines	Coverage Δ
core/nurse_scheduling/server/jobs/runner.py	83.33% <50.00%> (-3.34%)	⬇️

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