refactor(internal/librarianops/generate): move github functions to its own file

[miguelvelezsa]

Extracting github functions from generate and put them in its own file since upgrade command also needs them.

Also created function uploadToGithub, this functions make easier all the steps needed to upload changes to github. This function will be used in upgrade and generate, the changes for it will be in follow up PR.

For #3911.

Note: coverage complaint is related to generate tests, not to the new file.

[gemini-code-assist]

Code Review

This pull request is a good refactoring that moves GitHub-related utility functions into their own file, internal/librarianops/github_utils.go, improving separation of concerns. The addition of tests for these new utilities is also a positive change. However, I've identified a few issues. There's a critical issue with the new branch name generation logic that could cause failures if the tool is run multiple times a day. I've also noted some areas for improvement regarding redundant code, a minor style guide violation, and a bug in the new tests.

[codecov]

Codecov Report

❌ Patch coverage is 73.52941% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.15%. Comparing base (a29479b) to head (8abc5e1).

Files with missing lines	Patch %	Lines
internal/librarianops/generate.go	10.00%	7 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4689      +/-   ##
==========================================
+ Coverage   79.10%   79.15%   +0.04%     
==========================================
  Files         111      112       +1     
  Lines        9420     9436      +16     
==========================================
+ Hits         7452     7469      +17     
  Misses       1453     1453              
+ Partials      515      514       -1     

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[julieqiu]

hey @miguelvelezsa, thanks for the PR. I’ve taken a look and would prefer to keep these functions in generate.go for the time being. As we previously discussed, I’d also like to avoid introducing mocks at this stage to keep the testing structure lean. Let's hold off on this refactor for now.

[julieqiu]

Avoid names like utils: https://github.com/googleapis/librarian/blob/main/doc/howwewritego.md#package-names