Switch to martinohmann difflib fork and colorize diff output

[kpengboy]

This would at least be a partial solution to #371.

I did not add the colorization to the cfgtest output, but I wonder if I should.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 54.51%. Comparing base (6b9e153) to head (f3f1624).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/engine/label/diff.go	0.00%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (50.00%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #423      +/-   ##
==========================================
- Coverage   54.52%   54.51%   -0.01%     
==========================================
  Files          53       53              
  Lines        4457     4459       +2     
==========================================
+ Hits         2430     2431       +1     
- Misses       1886     1887       +1     
  Partials      141      141              

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[github-actions]

This pull request is stale because it has been open for 30 days without activity.
This will be closed in 7 days, unless you add the 'lifecycle/keep-alive' label or comment.

[kpengboy]

keepalive

[mbrt]

Nice, thanks! I can't immediately see why, but I tested manually, and it looks like gmailctl diff --color=never still colorizes the output. Could you double-check? Maybe I'm missing something.

[kpengboy]

Sorry about that. I fixed it so label diffs respect --color too.

Also, would you want a --color=always option to be implemented? If so we would have to implement the colorization logic ourselves instead of using the martinohmann difflib fork, but it doesn't seem very complicated to do

[mbrt]

@kpengboy I think this looks good enough, thanks!
Could you please rebase, resolve the conflicts and fix the tests? After that we can merge