feat: Server#query_members

[Droid00000]

Summary

This PR adds a#query_members method to allow you to get multiple members by user ID in one go. It uses the REQUEST_GUILD_MEMBERS opcode with the user_ids parameter to do this. Example usage:

ids = DB[:some_table].where { age > 12 }.all

result = event.server.query_members(ids: ids.map { it[:id] }) # => QueriedMembers

Added

Server#query_members
Discordrb::QueriedMembers

Changed

Pass the nonce and not_found data from the chunk to Server#process_chunk so the code can tell the difference between query requests, and when we are chunking the entire members list.

[Droid00000]

Should be superseded by #458.