[NIP-01] Multiple values for filter conditions

[scsibug]

Currently, with only one value allowed in a filter condition for id and kind, subscriptions are unnecessarily large.

A common use case for a client is to request all the profile, metadata, text notes, and deletion events for a set of followed pubkeys. Constructing this subscription for 100 addresses requires repeating the address in a filter for kind: 0, kind: 1, etc., leading to 400 addresses in the `REQ' message.

Allowing ids and kinds to be treated similarly to authors would allow clients to search across multiple event types without unnecessary duplication in the query. This would lead to significant bandwidth savings for clients and relays.