* fix(attachments): enforce quota at v2 metadata reservation
POST /ciphers/<id>/attachment/v2 persisted client-declared fileSize without
checking USER_ATTACHMENT_LIMIT or ORG_ATTACHMENT_LIMIT, allowing a writer to
exhaust org/user quota via metadata-only reservations before uploading bytes.
Extract shared quota arithmetic into attachment_quota_remaining and use it
from post_attachment_v2 (size_adjust=0) and save_attachment so both paths
stay consistent. Add unit tests covering limit, size_adjust, and the v2
over-quota rejection case.
* Remove unneeded tests and simplify
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Co-authored-by: Daniel García <dani-garcia@users.noreply.github.com>
