rust: Move PyBytesWithData out of copy-tracing code...
rust: Move PyBytesWithData out of copy-tracing code
So we can use it in other places to.
Replace its `.data()` method with the `Deref<Target = [u8]>` trait,
allowing this type to be used in generic contexts.
Rename the type accordingly.
Differential Revision:
https://phab.mercurial-scm.org/D11395