core: Add AnyUser field to DelegateRequest and pass to cache calls

keycache: Add AnyUser parameter to AddKeyFromRecord function signature

keycache_test: Add tests for AnyUser and update AddKeyFromRecord calls

cryptor: Update tests to AddKeyFromRecord to reflect API update

cmd/ro: Add bool flag for anyUser parameter

Note: This commit was further amended to change the AddKeyFromRecord
API to accept keycache.Usage as a parameter, which will make updating
usage simpler in the future.

keycache: Remove deprecated behavior in Usage.matches()

core: Add check during delegation for a User list or the AnyUser flag

tests: Add parameters to conform to new delegation requirements

core: Add unit tests scenarios

core: Check for a non-nil, but empty, Users list

keycache: Add unit tests

Output before change:
cryptor/cryptor_test.go:112:
github.com/cloudflare/redoctober/keycache.Usage composite literal uses
unkeyed fields