Function inline_cast

pub(crate) fn inline_cast<A, B>(input: *const A) -> *const B

Cast pointers around before passing them in to functions; this is sometimes needed when a struct is used from bindgen (riot_sys::*) but passed to a C2Rust function that uses its own definition (riot_sys::inline::*).

Ideally this’d use what comes out of safe transmutation to statically show castability (or not be needed due to better collaboration between C2Rust and bindgen), but until that’s a thing, checking for sizes is the least we can do.

TBD: Make this into a compile time failure (first attempts failed due to “use of generic parameter from outer function” errors). Anyhow, if the check passes, the function essentially becomes a no-op.