Use db.ListOptions directly instead of Paginator interface to make it easier to use and fix performance of /pulls and /issues (#29990)

This PR uses `db.ListOptions` instead of `Paginor` to make the code
simpler.
And it also fixed the performance problem when viewing /pulls or
/issues. Before the counting in fact will also do the search.

---------

Co-authored-by: Jason Song <i@wolfogre.com>
Co-authored-by: silverwind <me@silverwind.io>

models/issues/issue_stats.go

@@ -68,13 +68,17 @@ func CountIssuesByRepo(ctx context.Context, opts *IssuesOptions) (map[int64]int6
 }
 
 // CountIssues number return of issues by given conditions.
-func CountIssues(ctx context.Context, opts *IssuesOptions) (int64, error) {
+func CountIssues(ctx context.Context, opts *IssuesOptions, otherConds ...builder.Cond) (int64, error) {
 	sess := db.GetEngine(ctx).
 		Select("COUNT(issue.id) AS count").
 		Table("issue").
 		Join("INNER", "repository", "`issue`.repo_id = `repository`.id")
 	applyConditions(sess, opts)
 
+	for _, cond := range otherConds {
+		sess.And(cond)
+	}
+
 	return sess.Count()
 }