fix(releases): paginate GitHub client compare_commits to avoid 250-commit limit

[srest2021]

Per https://sentry.slack.com/archives/C08AZ3MD2EQ/p1770657631215169

Our customers are experiencing problems with missing commits on their releases, and the limit seems to be 250 commits. This is because we use GitHub's compare_commits endpoint, which is limited to 250 commits when unpaginated. Here we paginate the endpoint to make sure we get the complete commits list.

---

Complete flow from sentry-cli to getting the fetched release commits:

1. sentry-cli releases set-commits --auto resolves head shas from local git remotes via find_heads()
2. authenticated_api.set_release_refs() sends a put request with the resolved shas to /organizations/{org}/releases/{version}/, or OrganizationReleaseDetailsEndpoint.put()
3. OrganizationReleaseDetailsEndpoint.put() calls release.set_refs()
4. Release.set_refs() calls fetch_commits() task
5. fetch_commits() calls provider.compare_commits(), for GitHub that would be this function, which then hits the GitHub compare_commits endpoint.
6. Now that we have <=250 commits we store the author info then set that release's commits (thus creating CommitAuthors using the stored author info from the fetched commits, and linking Commit and CommitAuthor to ReleaseCommit)
7. Finally, we update release.authors to contain all the author ids for the ReleaseCommits for this release
8. Whenever we serialize a release, _get_authors_metadata() uses those author ids to query the corresponding CommitAuthor objects