make writer/reader types owned

[milyin]

Describe the release item

The types z_bytes_writer_t, z_bytes_reader_t are copyable according to their names. But they wraps Rust types ZBytesWriter/ZBytesReader which are not copyable.
The behavior of parallel reading/writing to multiple readers/writers is not defined.
There should be one and only one reader or writer for z_owned_bytes_t at any moment.
So we have to:

• make z_bytes_writer_t, z_bytes_reader_t owned to protect from copying
• (not right now, but it would be nice to have) - fail on creation e.g. z_owned_bytes_writer_t if another one exists

[milyin]

After discussion with @DenisBiryukov91 the following plan was proposed:

• the writer becomes z_owned_bytes_writer_t. The construction of the writer (in append case) consumes z_owned_bytes_t with move operation. This guarantees that no other writer can be created for the same ZBytes. After finishing writing the function e.g. z_close_writer which consumes writer and constructs updated z_owned_bytes_t should be called
• the reader remains as is, like e.g. z_slice_iterator_t. It's copyable, multiple readers for same z_owned_bytes_t are allowed

This proposal is similar to this attempt to fix the same issue in #675