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>

modules/indexer/issues/db/db.go

@@ -78,6 +78,17 @@ func (i *Indexer) Search(ctx context.Context, options *internal.SearchOptions) (
 		return nil, err
 	}
 
+	// If pagesize == 0, return total count only. It's a special case for search count.
+	if options.Paginator != nil && options.Paginator.PageSize == 0 {
+		total, err := issue_model.CountIssues(ctx, opt, cond)
+		if err != nil {
+			return nil, err
+		}
+		return &internal.SearchResult{
+			Total: total,
+		}, nil
+	}
+
 	ids, total, err := issue_model.IssueIDs(ctx, opt, cond)
 	if err != nil {
 		return nil, err