refactor: migrate from github3.py to PyGithub

[jmeridth]

What/Why

Migrate from github3-py to PyGithub>=2.6.0, aligning with the 6 sibling OSPO repos (cleanowners, measure-innersource, pr-conflict-detector, evergreen, contributors, stale-repos) that have already completed this migration.

Proof it works

• 194 tests pass with 100% coverage
• All pre-commit hooks pass

Risk + AI role

Medium -- touches auth, search, and all metric calculation modules. All code AI-assisted (Claude Opus 4.6) following established patterns from sibling repo PRs.

Review focus

• Auth module changes (App auth, token auth, GHE paths)
• PyGithub object access patterns (NamedUser.login vs dict, Label.name vs dict, native datetime handling)

Readiness Checklist

Author/Contributor

• If documentation is needed for this change, has that been included in this pull request
• run make lint and fix any issues that you have introduced
• run make test and ensure you have test coverage for the lines you are introducing

[Copilot]

Pull request overview

This PR migrates the action’s GitHub API client from github3.py to PyGithub>=2.6.0, updating the authentication flow, search layer, and metric-calculation modules to use PyGithub’s object model and datetime handling.

Changes:

• Replace github3.py usage with PyGithub types and access patterns across auth, search, and metric modules.
• Update metric logic to use native datetime fields from PyGithub objects instead of ISO string parsing.
• Refresh unit tests and dependency locks to reflect the new client library and object shapes.

Reviewed changes

Copilot reviewed 25 out of 27 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
uv.lock	Removes github3-py and locks pygithub (+ transitive deps like pynacl).
pyproject.toml	Swaps runtime dependency from github3-py to PyGithub>=2.6.0 and drops direct requests / types-requests.
auth.py	Reworks PAT + GitHub App auth to use PyGithub Auth / GithubIntegration.
search.py	Ports issue search and exception handling to GithubException.
issue_metrics.py	Updates per-issue metric extraction to PyGithub issue/PR fields and helpers.
labels.py	Updates label event parsing (event.label.name) and datetime arithmetic.
pr_comments.py	Updates comment/review-comment retrieval to PyGithub APIs (get_comments, get_review_comments).
most_active_mentors.py	Ports comment/review iteration to PyGithub and adds explicit max-eval limiting.
time_to_ready_for_review.py	Uses Issue.get_events() for ready-for-review event detection.
time_to_merge.py	Switches to PyGithub PullRequest and native datetime fields.
time_to_first_review.py	Uses PullRequest.get_reviews() and PyGithub user objects.
time_to_first_response.py	Uses Issue.get_comments() / PullRequest.get_reviews() and native datetime fields.
time_to_close.py	Uses native datetime fields for issue close duration calculation.
time_in_draft.py	Ports PR draft tracking logic to PyGithub (as_pull_request, get_events).
test_auth.py	Updates auth tests to mock PyGithub Auth, Github, and GithubIntegration behavior.
test_search.py	Updates search tests to use GithubException and new search return shapes.
test_issue_metrics.py	Updates issue/PR mocks to match PyGithub field shapes and datetime types.
test_time_to_ready_for_review.py	Updates event access to get_events().
test_time_to_first_review.py	Updates review access to get_reviews() and datetime inputs.
test_time_to_first_response.py	Updates comment/review accessors and user shapes for PyGithub.
test_time_to_close.py	Updates to use datetime objects for created/closed timestamps.
test_time_in_draft.py	Updates mocks to use get_events() / as_pull_request() and PyGithub-like issue shape.
test_labels.py	Updates label mocks to .name attribute objects and datetime fields.
test_pr_comments.py	Updates to PyGithub comment/review-comment accessors.
test_most_active_mentors.py	Updates comment/review accessors and adds review limit branch coverage.
.github/linters/.python-lint	Removes suggestion-mode setting from pylint config.
.coveragerc	Formatting-only change (no behavioral change).

[zkoppert]

A few follow-ups from a closer look at the migration, mostly around the search rate-limit handling and dependency declarations. I left the specifics inline.

[zkoppert]

🚀