Handshake-runner should allow unbounded FIFOs

The current implementation of the handshake runner implicitly has one buffer place per operation. This is sufficient for models that are generated from the standard-to-handshake conversion, but may not be sufficient
for more general models.
Probably the right path forward is to implement a multi-threaded executable, either in a similar style to the handshake-runner, or through some lowering path (e.g. async dialect -> LLVM + coroutines -> binary) with dynamically growing fifos. Note that a bound can still be useful to detect improperly constructed designs.

Start by locating the handshake-runner implementation and understanding its one-buffer-per-operation assumption. Compare the proposed multithreaded executable approach with the async dialect to LLVM, coroutines, and binary path; done means general models can use dynamically growing FIFOs while an optional bound can still detect improperly constructed designs.

Written by the indexing model from the issue text.