[Task]: Use tox built sdist instead of creating sdist and passing it via --installpkg

### What needs to happen?

Tox has ability to create sdist in an virtualenv. We need to use that capability since we run unit tests using tox. Also, doing this will free us from building our own sdist and passing it via the `--installpkg` to tox

### Issue Priority

Priority: 2 (default / most normal work should be filed as P2)

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