Simplify binary data handling in ps backend.

[anntzer]

• bytes.hex() can now perform linewrapping itself, so use that in
  draw_image.
• draw_gouraud_triangles can rely on PostScript's hexstring format
  (<...> instead of (...)) and thus on bytes.hex() too. This makes
  _quote_ps_string fully unused, thus tweak the deprecation of
  quote_ps_string.

PR Summary

PR Checklist

Tests and Styling

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

• New features are documented, with examples if plot related.
• New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).
• Documentation is sphinx and numpydoc compliant (the docs should build without error).

[oscargus]

The only potential "problem" is that the deprecation note says: "Vendor the code of the similarly named private functions if you rely on these functions." https://github.com/matplotlib/matplotlib/blob/main/doc/api/next_api_changes/deprecations/22797-OG.rst

But hopefully people will understand anyway (there are several functions deprecated, so probably not worthwhile special handling this one).

[oscargus]

Oh, if there is a suitable test to add that would be great! (Or are the lines actually tested despite the report?)

[anntzer]

It is quite possible that this is actually not tested; will add a test...

[anntzer]

Test added.