Parallelize `tests\test.ps1`.

[python-processing-unit]

Currently, test.ps1 runs each test sequentially, and reports the success or failure of that test upon it's completion.

Instead of running the tests sequentially, test.ps1 will spawn a number of threads equal to the number of logical processors on the machine it is running on minus one, or one, whichever is greater. Each thread will be assigned a single test which it will run, in alphabetical order. Once it has completed that test, it is assigned the next test in alphabetical order.

Instead of reporting the status of each individual test upon it's completion, test.ps1 will show "/ test completed, remaining." on a single line, which is updated every time a test is completed.

test.ps1 remains otherwise unchanged.