0.25.0

Synced to flipcash2-protobuf-api@53316c0e,
picking up #165.
activity.v1, intent.v1 and messaging.v1 moved.

This release lets the receiver of a DM's opening payment send it back. Nothing existing changed
on the wire. The source breaks are three new oneof cases, each appended after the existing ones.

Breaking

• activity.v1.DirectlySentCryptoNotificationMetadata and ReceivedCryptoNotificationMetadata
  each gain returned_payment (field 5) in their oneof, and intent.v1.ChatMetadata's oneof
  gains return_payment (field 7). An exhaustive switch over the Swift oneof, or a when over
  Kotlin's *Case without an else, needs a case for each before it compiles. Code that reads
  these oneofs through has*() checks compiles unchanged and drops the new case silently.

Added

• messaging.v1.Messaging.GetCashMessageReturnStatus, with its request and response.
  Result is OK, DENIED, NOT_FOUND (0–2) and Status is UNKNOWN, AVAILABLE,
  RETURNED (0–2). RETURNED never changes again, so a client can stop polling once it sees
  it. payment_intent_id is set only on OK, and only for the message's single_receiver.
• messaging.v1.CashContent.payment_return (field 7), of type CashContent.Return with
  independent offer and return_of. Return.Offer is empty: its presence is the offer.
  Today only the cash message that opened a DM carries one. A message with return_of set
  returns the payment of the message it names, so a client that sees it can stop offering a
  return on that message.
• intent.v1.ChatMetadata.ReturnPayment (message_id). The return is a SendPublicPayment
  from the original message's single_receiver back to its sender, in the same DM, for the
  same currency, mint and native amount. Its intent ID must be the server-issued
  payment_intent_id from GetCashMessageReturnStatus, not one the client generates. The
  server refuses any other ID, which is what keeps a payment returnable once across retries
  and devices. Treat that ID as private until the payment is made: anyone who uses it first
  blocks the return.
• activity.v1.ReturnedPayment (chat_id, message_id), naming the DM and the cash message
  whose payment was returned. The server doesn't update it afterwards, so the message may since
  have been deleted.

Unchanged

Nothing was renumbered. No service, RPC, field or enum case was removed or changed type.