itest: test second-level HTLC revocation in breach scenario

Extend the custom_channels_breach integration test to cover revoked
HTLC outputs that have been advanced to second level. The test now:

- Creates hodl invoices on both sides to place HTLCs on the commitment
  before the DB backup (breach state).
- Settles the hodl invoices and sends an additional keysend to revoke
  the HTLC state.
- Suspends Charlie before the breach so Dave can advance his HTLCs to
  second level without Charlie's justice tx interfering.
- Mines ~100 blocks in batches to let Dave's HTLC timeout resolvers
  broadcast pre-signed second-level transactions.
- Resumes Charlie who detects the breach and sweeps commitment outputs
  plus second-level HTLC outputs.

Also adds a dedicated Zane node as proof courier (stays online when
Charlie is suspended) and SuspendNode to IntegratedNetworkHarness.

Author: GeorgeTsagk