Make smoldot resilient to malicious parachain runtimes

[tomaka]

If a parachain runtime contains an infinite loop, smoldot, being single-threaded, will be stuck forever.

[tomaka]

Note that Substrate does this by spawning the executor in a separate process. We obviously can't (and, even if we could, don't want to) do that.

[tomaka]

This can be done with wasmtime using the fuel system, but not with wasmi.