Pytest-blender

- Don't show ugly traceback executing `pytest --help`.
- Don't show debug output retrieving Python Blender location with `pytest-blender` CLI.
- Avoid to display a warning retrieving Python Blender location in Blender >= 2.91.
- Improve Blender executable path discovering for MacOS.

- Fixed AttributeError trying to use the plugin disabling pytest cacheprovider plugin with `-p no:cacheprovider`.
- Show a proper error message if blender executable is not found.

Release first stable version. No changes.

Added new fixtures for easier addon testing:

- `install_addons_from_dir`
- `disable_addons`

- Improved setup metadata.
- Removed unused function.

- Added fixtures.
- Improved Blender subprocess isolation.