py: clean up lexer and reader if an import fails - #12369

Instead of changing the signature of mp_lexer_free how about creating a macro...

#define MP_DEFINE_NLR_CALLBACK_FUNCTION_1(ctx, f, d) \
nlr_jump_callback_node_call_function_1_t ctx = { \
    .func = (void (*)(void *))(f), \
    .arg = (void *)(d), \
}

Then usage is also less verbose.

Yeah, happy to make this change.

The reason I changed the signature was because I didn't want to risk any edge-case C incompatibility when casting a function to a different function pointer. I'm actually not sure of the rules here, do you know what is legal/allowed by the C standard with respect to casting function pointers?

I'm not aware of any compiler restrictions on casting functions pointers (e.g. https://stackoverflow.com/a/66206802/1976323). And I've seen plenty of code (including CPython extensions) that make casts like this. So I don't think there is anything to worry about here. We do lose some type safety, but it doesn't seem like something that would be easy to mess up in the first place.

I made this change.