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 58.8%. Comparing base (5270640) to head (031a3aa).
Report is 2 commits behind head on main.

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

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #205   +/-   ##
=====================================
  Coverage   58.8%   58.8%           
=====================================
  Files        194     194           
  Lines      15159   15171   +12     
=====================================
+ Hits        8922    8932   +10     
- Misses      6237    6239    +2     

Files	Coverage Δ
message_ix_models/tests/project/test_edits.py	100.0% <100.0%> (ø)
message_ix_models/project/edits/__init__.py	91.8% <77.7%> (-1.7%)	⬇️