Add exception safety to Rust code

[matejcik]

Currently Rust bindings calling Micropython functions do not install exception handlers. An exception raised by Micropython will skip and throw away the Rust context, which might lead to incorrectness in certain cases.

[matejcik]

Reading through rust-lang/rfcs#2625 and rust-lang/rust#58314, I'd be wary of using nlr_push in Rust directly.

For that matter, it prooobably means it's not safe to compile micropython with LLVM? Because nlr_push is not marked returns_twice. GCC also recognizes that attribute but per https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#returns_twice it doesn't do anything problematic as long as nlr_push is written correctly.

This means that we should trampoline through C, per @jpochyla's suggestion. That would entail either writing wrappers for all functions that can raise, or some macro magic, or maybe some sort of universal wrapper that takes a function pointer and variadic arguments??? Either way, it's not very nice.

[bosomt]

@matejcik can we move it to approved section ?

[matejcik]

done