[mycoliza]

We did it as a result of my suggestion, and I'll freely admit that it does seem pretty goofy!

The motivation, though, was that we wanted to write tests for the function that would run on a developer's machine using `cargo test`, and the Hubris kernel currently only compiles for the targets that we actually run Hubris on (various Cortex-M targets). So, if we want to write tests for that function, we would either need to move it to a crate that doesn't contain Cortex-M-only code, or litter the whole kernel with `#[cfg(not(test))]` attributes so that most of it doesn't compile when building tests. This felt much less unpleasant than conditional compilation. We're hoping that, eventually, other complex-but-not-architecture-specific kernel code will end up in the `kerncore` crate as well so that we can write tests for it, too, so eventually it won't be a crate with only one function...

I do think that there's room for tooling improvement to make writing host-platform tests for `#![no_std]` Rust that gets cross-compiled to another platform, but I don't have any particularly concrete ideas for what that would look like. For now, at least, putting it in a separate crate lets us have our tests --- and those tests let us ensure that some of the function's edge cases are handled correctly, so I do think it was worth it.