Add new obsolete variable mappings for pulse plant parameters

[chris-ashe]

This pull request adds new mappings to the obsolete variable translation dictionary in obsolete_vars.py, helping to map several time-related legacy variable names to their updated equivalents.

New obsolete variable mappings:

• Added mappings for time-related variables, including t_fusion_ramp, t_current_ramp_up, t_current_ramp_down, t_between_pulses, t_precharge, and t_burn, translating them to their new standardized names in the dictionary.## Description

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.06%. Comparing base (0519605) to head (160bbec).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3951   +/-   ##
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  Coverage   46.06%   46.06%           
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  Files         123      123           
  Lines       28467    28467           
=======================================
  Hits        13114    13114           
  Misses      15353    15353           

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