3258 add divertor and fwblanket lifetimes to st availability model

[j-a-foster]

Description

This adds the divertor and blanket lifetimes to the ST availability model. To streamline things, the divertor lifetime calculation was converted to its own function and inserted where the calculation was previously present in all availability models.

Checklist

I confirm that I have completed the following checks:

• My changes follow the PROCESS style guide
• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made.
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly.
• I have added documentation for my change, if appropriate.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 72.72727% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 29.57%. Comparing base (ec3c1f5) to head (9b41186).
⚠️ Report is 587 commits behind head on main.

Files with missing lines	Patch %	Lines
process/availability.py	72.72%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3414      +/-   ##
==========================================
+ Coverage   29.51%   29.57%   +0.05%     
==========================================
  Files          77       77              
  Lines       19049    19078      +29     
==========================================
+ Hits         5622     5642      +20     
- Misses      13427    13436       +9     

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[chris-ashe]

LGTM