NeuralCompression 0.2.1 Release, fixes for build system

This release covers a few small fixes from PRs #171 and #172.

Dependencies

• To retrieve versioning information, we now use importlib. This is included only with Python >= 3.8, so NeuralCompression will now only run on versions of Python at least as recent as 3.8. (#171).
• Install requirements are flexible, whereas dev requirements are fixed (#171). This should improve CI stability while allowing researchers flexibility in tuning their research environment while using NeuralCompression.
• torch has been removed as a build dependency (#172).
• Other build dependencies have been modified to be flexible (#172).

Build System

• C++ code from _pmf_to_quantized_cdf introduced compilation requirements when running setup.py. Since we didn't configure our build system to handle specific operating systems, this caused a failed release upload to PyPI. The build system has been altered to use torch.utils.cpp_extension.load, which defers compilation to the the user after package installation. We would like to improve this further at some point, but the modifications from #171 gets the package stable. Note: there is a reasonable chance this could fail on non-Linux OS's such as Windows. Those users will still be able to use other package features that don't rely on _pmf_to_quantized_cdf.

Other

• Fixed a linting issue where isort was not checking in CI if packages were properly sorted. (#171).
• Fixed a random test issue (#171).