This is theoretically simple. Currently we are blocking on calculating whether there are remote servers we need to send to, but we have a separate list of servers, so we just need to update the code to use it

Subtasks

• Faster joins: Creating events from local users: Track the set of forward safe chain events and use them as prev_events #14057
• Faster joins: Creating events from local users: Don't block. Send events to the separate list of servers. #14058
• Faster joins: Creating events from local users: Answer queries over federation where we are obligated to answer #14059