python: pytest support is not exported from fbcode

[lf-]

I would like to be able to build and test python code with buck2 outside Facebook. This seems to be possible, however, it requires (as used by buck2's //tests at least):

load("@fbcode_macros//build_defs:native_rules.bzl", "buck_filegroup")
load("@fbcode_macros//build_defs:python_pytest.bzl", "python_pytest")

These are not exported anywhere that I know of. They would be very helpful to have available to make meaningful use of buck2, so I would really appreciate them being exported.

This would also possibly allow slightly more of the Sapling test suite to run? Unclear.