NIP-09-PR: allow gift wrap recipients to request deletion of their own copy

[geralt-debugs]

NIP-09 currently requires that the pubkey of a kind:5 deletion request match the pubkey of the event being deleted. This works for events a user creates, but not for gift wraps (kind:1059), which are authored by an ephemeral random key even though they are addressed to a specific recipient via a p tag.

This PR extends NIP-09 to allow a gift wrap recipient to request deletion of their own copy. The rule is narrow and explicit: a kind:5 event may reference a kind:1059 event when the requester's pubkey appears in a p tag of that gift wrap and the k tag is "1059". In all other cases the existing NIP-09 author-matching rule is unchanged.

Since each NIP-17 recipient receives a separately-wrapped copy of a message, deleting one user's gift wrap has no effect on copies addressed to others. No new event kind is introduced.

Use cases

1. Users might want to remove spam from their inboxes/invites/etc
2. Users might simply want to cleanup their inboxes/invites/etc
3. Users might want to delete a message sent by someone else