feat(cbf):

  add auto-restart with exponential backoff (#10)

* refactor(cbf): extract build_cbf_node helper and add wallet reference
* feat(cbf): auto-restart bip157 node with exponential backoff
* feat(cbf): add liveness check before returning requester
* fix(cbf): clean up scan state on filter scan failure
* fix(cbf): add per-block-fetch timeout to wallet sync

Author: febyeji