RegValue should contain Cow<[u8]>, not Vec<u8>

[Enyium]

In my abstracting write-function, I prevent having to unnecessarily clone the byte array this way:

pub fn write_reg_bin_value(
    reg_value_path: &RegValuePath,
    bytes: &Vec<u8>,
) -> Result<(), io::Error> {
    let key = RegKey::predef(reg_value_path.hkey)
        .open_subkey_with_flags(reg_value_path.subkey_path, KEY_SET_VALUE)?;

    let unsafe_reg_value = ManuallyDrop::new(RegValue {
        vtype: RegType::REG_BINARY,
        // Unsafely double-owned `Vec`.
        bytes: unsafe { Vec::from_raw_parts(bytes.as_ptr() as _, bytes.len(), bytes.capacity()) },
    });

    // A panic would leak the reg value, but at least not cause a double-drop.
    let result = key.set_raw_value(reg_value_path.value_name, &unsafe_reg_value);

    // Drop only parts in fact owned. Use `ManuallyDrop` like `Vec::into_raw_parts()`, which is available in nightly Rust (as of Nov. 2023).
    let RegValue { bytes, .. } = ManuallyDrop::into_inner(unsafe_reg_value);
    let _ = ManuallyDrop::new(bytes);

    result?;
    Ok(())
}

This is quite hacky, of course.

When winreg generates a RegValue by reading it from the registry, it would use Cow::Owned. But when writing one with RegKey::set_raw_value(), which borrows it immutably anyways, Cow::Borrowed would suffice, so you don't have to unnecessarily clone the value, just for an immutalbe borrow!