[Epic] M4: Faster Solarkraft

[thpani]

Extend Apalache to accept verification requests on a JSON/REST endpoint and use this endpoint for integration with Solarkraft.

Context: Solarkraft currently spawns a fresh Apalache process for each transaction it verifies. Since Apalache runs on JVM, this incurs a significant startup cost. Apalache supports a protobuf-based server mode that comes without this startup penalty, but only accepts unstructured TLA+ (not the structured Apalache JSON IR produced by Solarkraft).

Deliverables: code (+ tests), performance evaluation