[API sync] Handle sweep_tx event and swept_vtxos from GetTransactionsStream (arkd#988)

[arkanaai]

Context

arkd#988 (Forward sweep txs event in transaction stream) was merged to master at 2026-03-23T09:16:57Z.

What changed in arkd

Two additive changes to the GetTransactionsStream gRPC + REST API:

1. New sweep_tx event type on GetTransactionsStreamResponse (field 4)

message GetTransactionsStreamResponse {
  oneof data {
    TxNotification commitment_tx = 1;
    TxNotification ark_tx = 2;
    Heartbeat heartbeat = 3;
    TxNotification sweep_tx = 4;  // NEW
  }
}

2. New swept_vtxos field on TxNotification (field 6)

message TxNotification {
  ...
  repeated Outpoint swept_vtxos = 6;  // NEW
}

Required updates in this SDK

• Regenerate protobuf from updated service.proto in arkd (NArk.Core/Transport/GrpcClient/Protos/)
• Handle SweepTx case in GetTransactionsStream response dispatcher
• Expose SweptVtxos on the .NET TxNotification model
• Add a SweepTx event/notification type if needed
• Update tests

Reference

• arkd PR: Transaction stream: add sweep tx event arkd#988
• Commit: eeb0baef6937b7544e0f659edbeee58f8aa2a90e

/cc @Kukks