`lightning-liquidity` Persistence Tracking Issue

[tnull]

• Prefactors: lightning-liquidity: Pre-/Refactors to prepare for persistence #4008
• Add service handler and event queue serialization logic: lightning-liquidity: Add serialization logic, persist service state #4059
• Add boilerplate to account for KVStore and KVStoreSync variants: lightning-liquidity: Add serialization logic, persist service state #4059
• Wire up background processor to drive general persistence lightning-liquidity: Add serialization logic, persist service state #4059
• Avoid re-persisting peer states if no changes happened (needs_persist flag everywhere) lightning-liquidity: Add serialization logic, persist service state #4059
• Persist in-line for very important calls that need to be persisted before we return lightning-liquidity: Add serialization logic, persist service state #4059
• Add roundtrip test coverage lightning-liquidity: Add serialization logic, persist service state #4059
• Allow to drop/remove historical peer states
• (optional) Look into parallizing persistence (e.g., we could persist batches of peer states at the same time, instead of persisting them sequentially) (first step done in lightning-liquidity: Add serialization logic, persist service state #4059)
• KVStore::remove on peer state pruning lightning-liquidity: Eventually archive or remove persisted state #4084