refactor: use handle pattern for Kyoto client

refactor: use handle pattern for Kyoto client

Refactor KyotoClient to use a KyotoClientHandle struct instead of
Box<LightClient>. Previously, the Box<LightClient> was consumed
when destructured in sync_kyoto_client, preventing the function
from being called multiple times or borrowed. With the handle
pattern, sync_kyoto_client now takes &mut KyotoClientHandle,
allowing it to be borrowed and reused.

This also allows the node to be started at creation time in
new_blockchain_client rather than during sync, making the client
ready for use immediately after creation.

- Add KyotoClientHandle struct containing requester and
  update_subscriber
- Move node startup and logger spawning to new_blockchain_client
- Update sync_kyoto_client to accept &mut KyotoClientHandle
  instead of consuming Box<LightClient>