fix: Add imports to allow experimental_python_import_all_repositories

[ewianda]

This fixes breakage for users of this repository when --experimental_python_import_all_repositories=false is set, which the Bazel team would like to do in bazelbuild/bazel#2636.

See also bazelbuild/rules_python#792

Without this change, users get the error:.

runfiles/rules_pycross/pycross/private/tools/wheel_installer.py", line 14, in <module>
    from pycross.private.tools import namespace_pkgs
ModuleNotFoundError: No module named 'pycross'

[jvolkman]

Thanks! I'll need to investigate this test failure.

[ewianda]

Hi @jvolkman was wondering if you had a chance to look at this.

[jvolkman]

I fixed the test issue in main, so I'll merge this now.