remove CStr8 and replace by libcore::ffi::CStr

[phip1611]

This is a cleanup PR. It removes everything related to CStr8. I replaced it with core::ffi::CStr which is available since Rust 1.62.0.

[nicholasbishop]

One concern I have here is encoding. The CHAR8 type in the UEFI spec (section 2.3.1 Data Types) says: "1-byte character. Unless otherwise specified, all 1-byte or ASCII characters and strings are stored in 8-bit ASCII encoding format, using the ISO-Latin-1 character set."

As far as I can see though, CStr doesn't specify any particular encoding; it's just a null-terminated C string.

I'm not sure that the current code is correctly enforcing the latin-1 encoding (are all 255 non-null bit patterns actually valid as Char8::try_from implies?), and I've never actually used any of the APIs in UEFI that use latin-1 instead of UCS2, but I think there is still good reason to have a latin-1 type in uefi-rs.

[phip1611]

Couldn't we easily verify this by using the one-liner let _ = str::from_raw_parts(cstr.as_ptr(), cstr.len()).map_err(...)??

Ahh, there might be mismatches because UTF-8 would be allowed by that line but UEFI doesn't understand it..From that string slice, we could check if the length equals the number of chars, thus, there are no two-byte or four-byte characters in it 😅 then we have what we want

I analyzed the code lines where CStr8 is used. We are exposing the "PXE Base Code protocol" (struct BaseCode) which indeed has this type in its public API.

I do not insist on this change, but I always like code cleanups.

Hm.. the more I think about it: yeah, probably core::ffi::CStr is not what we want here in the public interface

[phip1611]

Closing this in favor of #506