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/issues/review_list.go

@@ -47,14 +47,9 @@ func (reviews ReviewList) LoadReviewersTeams(ctx context.Context) error {
 		}
 	}
 
-	teamsMap := make(map[int64]*organization_model.Team, 0)
-	for _, teamID := range reviewersTeamsIDs {
-		team, err := organization_model.GetTeamByID(ctx, teamID)
-		if err != nil {
-			return err
-		}
-
-		teamsMap[teamID] = team
+	teamsMap, err := organization_model.GetTeamsByIDs(ctx, reviewersTeamsIDs)
+	if err != nil {
+		return err
 	}
 
 	for _, review := range reviews {