Fix failure when running within a UV venv activated shell (tox-dev#66)

[pre-commit.ci] pre-commit autoupdate (tox-dev#58)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Fix interpreter (tox-dev#53)

Fix environment check (tox-dev#52)

Add PyPy support (tox-dev#51)

Pass sys.executable to `uv venv` if it is the same version (tox-dev#40)

* Pass sys.executable to `uv venv` if it is the same version

Support the case when pythonX.Y is not in the search path, but
it corresponds to the currently running Python interpreter.

This may happen if e.g. Tox is installed (along with tox-uv) in
a virtual environment that has been created with a Python interpreter
coming from a non-standard location, and then `tox` is invoked
directly from the virtual environment's `bin/` directory:

    [roam@straylight ~]$ mkdir ~/not-in-path

    [roam@straylight ~]$ uv venv -p /opt/some-vendor/python3/bin/python3 ~/not-in-path/venv
    Using Python 3.8.17 interpreter at: /opt/some-vendor/python3/bin/python3
    Creating virtualenv at: /home/roam/not-in-path/venv
    Activate with: source /home/roam/not-in-path/venv/bin/activate

    [roam@straylight ~]$ (set -e; . ~/not-in-path/venv/bin/activate; uv pip install tox tox-uv)
    ...snip...

    [roam@straylight ~]$ printf -- '%s\n' '[testenv]' 'package=skip' 'commands=python3 -c "print()"' > ~/not-in-path/tox.ini

    [roam@straylight ~]$ ~/not-in-path/venv/bin/tox -c ~/not-in-path/tox.ini
    py: venv /home/roam/not-in-path> venv/bin/uv venv -p 3.8 /home/roam/not-in-path/.tox/py/.venv
      × No Python 3.8 in `PATH`. Is Python 3.8 installed?
    py: exit 1 (0.01 seconds) /home/roam/not-in-path> venv/bin/uv venv -p 3.8 /home/roam/not-in-path/.tox/py/.venv pid=1059253
      py: FAIL code 1 (0.02 seconds)
      evaluation failed :( (0.11 seconds)

    [roam@straylight ~]$

* Let Ruff know that we try to use subprocess responsibly

* Tox is certainly installed during the test suite run

Add uv_resolution as testenv parameter (tox-dev#39)

* Add uv_resolution as testenv parameter

uv supports defining a custom resolution strategy, defaulting to
'highest', and allowing 'lowest' or 'lowest-direct' at the time of
writing, which provides an alternative to package constraints enabling
lowest direct or transitive dependencies to be installed.

This change provides a new 'uv_resolution' configuration option for test
environments, which if defined will apply the '--resolution' option to
uv to enable this behavior.

Implements tox-dev#28.

* Ensure call arguments match defined options for uv resolution

* Restrict uv resolution options to known values

uv currently supports "highest", "lowest", or "lowest-direct" as
resolution strategies, which we now validate.

* Document the new `uv_resolution` flag

* Use base type and post-process for uv_resolution

mypy expects the actual type for add_config, so we instead use
post-processing to validate the literal string against known options,
raising an error if otherwise.

* Test all valid and an invalid uv_resolution strategy

Validate package name of sdist/wheel/editable to be installed (tox-de…

…v#33)

Add the uv version into the --version (tox-dev#29)

Pass through often used environment variables (tox-dev#26)