Fix the wrong push commits in the pull request when force push (#36914)

Fix #36905

The changes focus on force-push PR timeline handling and commit range
calculation:
- Reworked pull-request push comment creation to use a new
`gitrepo.GetCommitIDsBetweenReverse` helper, with special handling for
force pushes (merge-base based range, tolerate missing/invalid old
commits, and keep force-push timeline entries).
- Added `Comment.GetPushActionContent` to parse push comment payloads
and used it to delete only non-force-push push comments during force
pushes.
- Removed the old `Repository.CommitsBetweenNotBase` helper from
`modules/git/repo_commit.go` in favor of the new commit ID range helper.
- Added tests for `GetCommitIDsBetweenReverse` (normal range, `notRef`
filtering, fallback branch usage) and expanded pull comment tests to
cover force-push edge cases.

<img width="989" height="563" alt="image"
src="https://github.com/user-attachments/assets/a01e1bc2-fa8a-4028-8a35-d484e601ff3b"
/>

---------

Signed-off-by: Lunny Xiao <xiaolunwen@gmail.com>
Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/agit/agit.go

@@ -282,12 +282,15 @@ func ProcReceive(ctx context.Context, repo *repo_model.Repository, gitRepo *git.
 		if err != nil {
 			return nil, fmt.Errorf("failed to load pull issue. Error: %w", err)
 		}
-		comment, err := pull_service.CreatePushPullComment(ctx, pusher, pr, oldCommitID, opts.NewCommitIDs[i], forcePush.Value())
-		if err == nil && comment != nil {
+
+		isForcePush := forcePush.Value()
+		comment, commentCreated, err := pull_service.CreatePushPullComment(ctx, pusher, pr, oldCommitID, opts.NewCommitIDs[i], isForcePush)
+		if err != nil {
+			log.Error("CreatePushPullComment: %v", err)
+		} else if commentCreated {
 			notify_service.PullRequestPushCommits(ctx, pusher, pr, comment)
 		}
 		notify_service.PullRequestSynchronized(ctx, pusher, pr)
-		isForcePush := comment != nil && comment.IsForcePush
 
 		results = append(results, private.HookProcReceiveRefResult{
 			OldOID:            oldCommitID,