optimize direct timeline (#7614)

* optimize direct timeline

* fix typo in class name

* change filter condition for direct timeline

* fix codestyle issue

* revoke index_accounts_not_silenced because direct timeline does not use it.

* revoke index_accounts_not_silenced because direct timeline does not use it.

* fix rspec test condition.

* fix rspec test condition.

* fix rspec test condition.

* revoke adding column and partial index

* (direct timeline) move merging logic to model

* fix pagination parameter

* add method arguments that switches return array of status or cache_ids

* fix order by

* returns ActiveRecord.Relation in default behavor

* fix codestyle issue