Make the light-client more robust to panics by using `panic=unwind`

[tomaka]

This isn't possible in Rust yet, but in principle we could use panic=unwind when compiling the wasm node. Then, the code could be tweaked in order to restart services if they die.

[tomaka]

rust-lang/rust#111322 is included in Rust 1.72

[tomaka]

Unfortunately, using rust-lang/rust#111322 seems incompatible with using wasm32-wasi-threads for #91

Or maybe we could do threads manually instead of using wasm32-wasi-threads.

[tomaka]

Ignoring the wasm-node, I think it's a good idea to do this in situations where the light client is embedded in a program where unwinding is enabled.

One blocker is the design of the "networking events receivers". It's not possible right now to create a new receiver in case the sync/runtime/etc service dies and takes the receiver with it in its death.
And similarly if the networking service dies things are complicated and a simple receiver is maybe not the most appropriate way.

[tomaka]

One issue with the latest comment is that it forces the UnwindSafe trait on Platform.
A bigger issue is (if I'm not mistaken) that async functions seem to generate futures that don't implement UnwindSafe.

[tomaka]

The first thing to do would be to refactor the RuntimeService to have a clear separate between foreground and background (which is something I think should be done no matter what).