Add oldest data (1991-1995) back to FERC Form 2 archiver

[e-belfer]

Overview

Closes #1259

What problem does this address?

• New FERC Online archive doesn't contain oldest FERC Form 2 data.

What did you change in this PR?

• Add back the old archiving method, just for the oldest years of data.

Question for reviewer

• Do we want to add the parts = all partition back for newer DBF and XBRL data?

Testing

How did you make sure this worked? How can a reviewer verify this?
Run the archiver and verify the oldest data is not deleted: https://github.com/catalyst-cooperative/pudl-archiver/actions/runs/32282792533

To-do list

• Update relevant documentation - like comments, docstrings, README, release notes, etc.
• Review the PR yourself and call out any questions or issues you have

[codecov-commenter]

Codecov Report

❌ Patch coverage is 40.00000% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.9%. Comparing base (700e1b3) to head (209fb55).

Files with missing lines	Patch %	Lines
src/pudl_archiver/archivers/ferc/ferc2.py	40.0%	12 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1284     +/-   ##
=======================================
- Coverage   60.0%   59.9%   -0.2%     
=======================================
  Files         67      67             
  Lines       3411    3430     +19     
=======================================
+ Hits        2049    2056      +7     
- Misses      1362    1374     +12     

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[zschira]

Looks good! I had just been meaning to do a test run locally before approving, which I've done now and seems to be working fine

[e-belfer]

@zschira any opinions about this?

Do we want to add the parts = all partition back for newer DBF and XBRL data?

[zschira]

Do we want to add the parts = all partition back for newer DBF and XBRL data?

I think it would make sense to add in for the DBF data since that is a meaningful distinction there, but since XBRL data isn't split into multiple partitions like this, it's probably fine to leave out there.