feat(sync-v2): Wait for sync internal methods to finish before initiating next syncing cycle

[msbrogli]

Motivation

Previously, the _run_sync() method checked for ongoing mempool syncs or open streamings to prevent concurrent cycle runs. Despite the presence of the _is_running: bool flag, it was prematurely marked as false due to mempool syncs and streamings returning at the start, not the end, of their execution. This led to complexity and potential errors in _run_sync(). This PR streamlines this process for better clarity and reliability.

Acceptance Criteria

1. Create the deferred _deferred_blockchain_streaming when we request the peer to open a block streaming.
2. Resolve the _deferred_blockchain_streaming when the streaming ends.
3. Create the deferred _deferred_transactions_streaming when we request the peer to open a transactions streaming.
4. Resolve the _deferred_transactions_streaming when the streaming ends.
5. Change run_sync_transactions() to wait for its streaming to end.
6. Change run_sync_blocks()to wait for its streaming to end.
7. Change mempool_manager.run() to return a deferred that is resolved when the execution is complete.

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

The base branch was changed.