Convert current drive vars to dataclass

[clmould]

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

❌ Patch coverage is 75.07331% with 85 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.74%. Comparing base (7a1cc86) to head (9c2806b).

Files with missing lines	Patch %	Lines
process/models/physics/current_drive.py	67.90%	26 Missing ⚠️
process/models/stellarator/heating.py	11.53%	23 Missing ⚠️
process/models/physics/bootstrap_current.py	0.00%	14 Missing ⚠️
process/models/physics/physics.py	11.11%	8 Missing ⚠️
process/models/physics/plasma_current.py	0.00%	4 Missing ⚠️
process/models/stellarator/stellarator.py	0.00%	4 Missing ⚠️
process/core/scan.py	0.00%	2 Missing ⚠️
process/core/solver/objectives.py	0.00%	2 Missing ⚠️
process/models/buildings.py	0.00%	1 Missing ⚠️
process/models/stellarator/initialization.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4252      +/-   ##
==========================================
- Coverage   50.86%   50.74%   -0.13%     
==========================================
  Files         151      151              
  Lines       29739    29662      -77     
==========================================
- Hits        15128    15051      -77     
  Misses      14611    14611              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.