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_test.go

@@ -0,0 +1,25 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package organization_test
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models/db"
+	org_model "code.gitea.io/gitea/models/organization"
+	"code.gitea.io/gitea/models/unittest"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_GetTeamsByIDs(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+
+	// 1 owner team, 2 normal team
+	teams, err := org_model.GetTeamsByIDs(db.DefaultContext, []int64{1, 2})
+	assert.NoError(t, err)
+	assert.Len(t, teams, 2)
+	assert.Equal(t, "Owners", teams[1].Name)
+	assert.Equal(t, "team1", teams[2].Name)
+}