1105 lifetime variables definitions

[j-a-foster]

Description

Fixes avail_2 not modifying component lifetimes in line with the calculated availability and made sure costs.py uses calendar years not FPY.

Checklist

I confirm that I have completed the following checks:

• 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.

[chris-ashe]

See comments

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 48.27586% with 15 lines in your changes missing coverage. Please review.

Project coverage is 27.21%. Comparing base (b68ac63) to head (2a09f3a).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
process/costs.py	33.33%	10 Missing ⚠️
process/availability.py	64.28%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3352      +/-   ##
==========================================
+ Coverage   27.11%   27.21%   +0.09%     
==========================================
  Files          76       76              
  Lines       17736    17756      +20     
==========================================
+ Hits         4810     4832      +22     
+ Misses      12926    12924       -2     

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