perf: improve Bytes::copy_to_bytes

[tisonkun]

Ref - https://greptime.com/blogs/2024-04-09-rust-protobuf-performance#step-5-why-is-bytes-slice-so-slow

We already use this tech for BytesMut, but not bring it for Bytes. Namely, reduce the overhead of slice.

impl Buf for BytesMut {
    ...
    fn copy_to_bytes(&mut self, len: usize) -> Bytes {
        self.split_to(len).freeze()
    }
}

[tisonkun]

cc @Darksonn

[braddunbar]

Nice! Great consolidation.

[tisonkun]

@braddunbar shall we merge this patch? Or it's still wait for further reviews?

[tisonkun]

Thank you!

[Darksonn]

Thank you for the PR :)