Use batch database operations instead of one by one to optimze api pulls (#32680)

Resolve #31492

The response time for the Pull Requests API has improved significantly,
dropping from over `2000ms` to about `350ms` on my local machine. It's
about `6` times faster.

A key area for further optimization lies in batch-fetching data for
`apiPullRequest.ChangedFiles, apiPullRequest.Additions, and
apiPullRequest.Deletions`.

Tests `TestAPIViewPulls` does exist and new tests added.

- This PR also fixes some bugs in `GetDiff` functions.
- This PR also fixes data inconsistent in test data. For a pull request,
the head branch's reference should be equal to the reference in
`pull/xxx/head`.

models/organization/team_list.go

@@ -131,3 +131,8 @@ func GetTeamsByOrgIDs(ctx context.Context, orgIDs []int64) (TeamList, error) {
 	teams := make([]*Team, 0, 10)
 	return teams, db.GetEngine(ctx).Where(builder.In("org_id", orgIDs)).Find(&teams)
 }
+
+func GetTeamsByIDs(ctx context.Context, teamIDs []int64) (map[int64]*Team, error) {
+	teams := make(map[int64]*Team, len(teamIDs))
+	return teams, db.GetEngine(ctx).Where(builder.In("`id`", teamIDs)).Find(&teams)
+}