contextzip 0.5.7 — cz update works with uv, pipx and venvs

Fixed

• cz update works with uv, pipx and virtual environments, not just
  plain pip. It detects how contextzip was installed (pip, pipx, uv tool,
  or a venv made by uv, which has no pip) and tries each installer that
  can upgrade the running Python in turn — pip, uv pip, pipx upgrade,
  uv tool upgrade — until the new version is actually installed. Outside
  a venv, a pip permission error is retried with --user.
• When every attempt fails, cz update lists each command it ran with its
  error, a hint for the likely cause (an OS-managed Python, a folder you
  can't write to, no pip or uv available), and the exact command to run
  by hand for your setup. It now exits non-zero on failure.