Update emissions accounting for trade

[junukitashepard]

CO2 emissions were not properly tracked for bilateralized trade flows through relation activity. This ensures that relation activity has proper emissions factors associated with them (negative for exports, positive for imports)

How to review

Relation activity for CO2 emissions tracking in trade should be transferred from edit to bare

PR checklist

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

[codecov]

Codecov Report

❌ Patch coverage is 84.61538% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.3%. Comparing base (1f7fe08) to head (5609668).
⚠️ Report is 165 commits behind head on main.

Files with missing lines	Patch %	Lines
...ssage_ix_models/tools/bilateralize/prepare_edit.py	84.6%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #496     +/-   ##
=======================================
- Coverage   73.3%   73.3%   -0.1%     
=======================================
  Files        301     301             
  Lines      24429   24440     +11     
=======================================
+ Hits       17914   17922      +8     
- Misses      6515    6518      +3     

Files with missing lines	Coverage Δ
...ssage_ix_models/tools/bilateralize/prepare_edit.py	89.5% <84.6%> (-0.3%)	⬇️

... and 1 file with indirect coverage changes

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