fix(sync-v2): Fix stream end messages for both blockchains and transactions

[msbrogli]

Motivation

Stream servers were being stopped in multiple places but sometimes without sending an end message or sending the wrong type of message.

Acceptance Criteria

1. Add StreamEnd.PER_REQUEST.
2. Introduce both stop_tx_streaming_server() and stop_blk_streaming_server() methods.
3. Update previous calls to send_transactions_end() to stop_tx_streaming_server().
4. Update previous calls to send_blocks_end() to stop_blk_streaming_server().
5. Fix internal errors in streamers always sending BLOCKS-END messages.
6. Fix handle_get_transactions_bfs() wrongfully sending BLOCKS-END message.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged