Apply 3 commits for 6.13.y

Hi Greg, Sasha,

Please consider applying the following commits for 6.13.y:

27c7518e7f1c ("rust: finish using custom FFI integer types") 1bae8729e50a ("rust: map `long` to `isize` and `char` to `u8`") 9b98be76855f ("rust: cleanup unnecessary casts")

They should apply cleanly.

This backports the custom FFI integer types, which in turn solves a build failure under `CONFIG_RUST_FW_LOADER_ABSTRACTIONS=y`.

I will have to send something similar to 6.12.y, but it requires more commits -- I may do the `alloc` backport first we discussed the other day.

Thanks!

Cheers, Miguel