Extend data handling for the EDITS transport MCE

[khaeru]

• Add .edits.PASTA, an ExoDataSource subclass for the PASTA transport activity data.
• More TBA.

How to review

TBA

PR checklist

• Continuous integration checks all ✅
• Add or expand tests; coverage checks both ✅
• Add, expand, or update documentation.
• Update doc/whatsnew.

[codecov]

Codecov Report

Attention: Patch coverage is 84.61538% with 2 lines in your changes missing coverage. Please review.

Project coverage is 77.4%. Comparing base (4fd6446) to head (228f512).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
message_ix_models/project/edits/__init__.py	77.7%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #205   +/-   ##
=====================================
  Coverage   77.4%   77.4%           
=====================================
  Files        217     217           
  Lines      16851   16863   +12     
=====================================
+ Hits       13048   13058   +10     
- Misses      3803    3805    +2     

Files with missing lines	Coverage Δ
message_ix_models/tests/project/test_edits.py	100.0% <100.0%> (ø)
message_ix_models/project/edits/__init__.py	93.1% <77.7%> (-1.8%)	⬇️

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