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/internal/tests/tests.go

@@ -77,6 +77,13 @@ func TestIndexer(t *testing.T, indexer internal.Indexer) {
 				assert.Equal(t, c.ExpectedIDs, ids)
 				assert.Equal(t, c.ExpectedTotal, result.Total)
 			}
+
+			// test counting
+			c.SearchOptions.Paginator = &db.ListOptions{PageSize: 0}
+			countResult, err := indexer.Search(context.Background(), c.SearchOptions)
+			require.NoError(t, err)
+			assert.Empty(t, countResult.Hits)
+			assert.Equal(t, result.Total, countResult.Total)
 		})
 	}
 }