PR: Overhaul unit tests to use np.testing.assert_allclose definition.

[KelSolaar]

Summary

This PR overhauls the unit tests to use np.testing.assert_allclose definition. We have been suffering hard to reproduce precision loss issues during multi-threaded unit tests and using np.testing.assert_allclose definition helps alleviate it, albeit in a disappointing way. With that said, np.testing.assert_allclose is recommended by Numpy over np.testing.assert_array_almost_equal thus this is a welcome switch.

Preflight

Code Style and Quality

• Unit tests have been implemented and passed.
• Pyright static checking has been run and passed.
• Pre-commit hooks have been run and passed.
• [N/A] New transformations have been added to the Automatic Colour Conversion Graph.
• [N/A] New transformations have been exported to the relevant namespaces, e.g. colour, colour.models.

Documentation

• [N/A] New features are documented along with examples if relevant.
• [N/A] The documentation is Sphinx and numpydoc compliant.