Replace `kernel::str::BStr` with `core::bstr::ByteStr`

[tamird]

This is brand new and still unstable (tracking issue rust-lang/rust#134915) but we should keep an eye on it and proactively request changes if we're going to need them.

This task is similar to (but should be simpler than) #1075.

[KunWuChan]

Hi, How shoud we do? Just replace the implement of BStr with ByteStr?
If need, I'll pleasure do it.

[tamird]

Working on this would be premature as ByteStr is very new. We would need to wait at least until our MSRV

linux/.clippy.toml

Line 3 in cf25bc6

msrv = "1.78.0"

is recent enough to contain the ByteStr APIs we need. That looks like it will be 1.86.0.

[KunWuChan]

Ok,I'll try to do that when msrv be 1.86.0.