Avoid use of centralised semaphore service

[michielbdejong]

We want LedgerLoops to be usable in an open network, so the way this prototype uses a centralised semaphore service is unacceptable. We hope to resolve this in Q1/Q2 of 2025, also adding some other robustness improvements, to move from this prototype to a minimum viable product, and from there to actual production use of LedgerLoops for obligation clearing in a peer-to-peer network setting.