Summary

This PR implements support for multi-spectral distributions in colour.spectral_similarity_index definition.

It should broadcast:

• sd vs sd
• sd vs msds
• msds vs sd
• msds vs msds (assuming that they are broadcastable)

References #1370.

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

• New features are documented along with examples if relevant.
• The documentation is Sphinx and numpydoc compliant.