Crossenv

Added
- Support for arbitrary platform tags via --platform-tag
- Correctly handle importlib.metadata
- Correctly map powerpc architecture variants
- Support Python freethreading build

Added
- Support for Python 3.11

Added
- Support for setuptools >= 61 (94)
- Support for Pypy (95)

Fixed
- Fixed typo in `mac_ver` (91)
- `sysconfig.get_platform()` for ppc64le (92)

Added
- Some support for pypy (82, 85)
- Crossenv will optimistically continue if it cannot query the compiler. (QNX,
etc.)

Added
- `--machine` argument to fine-tune apparent value of `os.uname().machine`

Fixed
- Fixed build failure when pip runs from a zip file.
- Fixed CI build due to master -> main branch switch in CPython.

Fixed
- Correctly set up crossenv environment with Python 3.10