PR: Performance improvements to colour.SpectralDistribution.wavelengths property and various definitions in colour.utilities.array module.

[tjdcs]

Summary

This PR makes small changes to improve the performance of several critical paths that are found throughout the code base. For example, tsplit and tstack are called very often. Additionally, the shape getter of SpectralDistribution is called very often in code that is manipulating spectral data. In one example calculating color rendering simulations, calling the .shape getter was responsible for around 10% of total execution time, but is now responsible for less than 0.1%

The particular examples that found these critical paths are not expected to be representative of all performance cases, none the less nearly all applications of colour-science should see some benefit.

Preflight

Code Style and Quality

• Unit tests have been implemented and passed.
• Mypy 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.

[KelSolaar]

Thank you! I left a few minor notes but LGTM otherwise!