Consider allowing Snaps to be multi-threaded

Using snaps for low latency high frequency trading brings a new set of problems. @chrisckwong821 has a theory that a single-threaded asynchronous Snaps might be too slow to be competitive and suggest allowing a multi-threaded environment.

To test that theory we should create some benchmarks. One benchmark mentioned was listening to multiple EVM chains (eg. Phantom / Ethereum) on local node at the same time and compare latency single-threaded / multi-threaded RPC requests.

No file or test is named. Start by locating the Snaps execution/runtime entry point and any existing benchmark harness, then define the local-node scenario for listening to multiple EVM chains and comparing single-threaded with multi-threaded RPC latency. Done means the benchmark results show whether multi-threading improves the stated workload.

Written by the indexing model from the issue text.