feat(radio-materials): update ITU materials to version 4

[jeertmans]

Hi!

Since version 4 of recommendation ITU-R P.2040 has been released, a number of materials have been added or extended compared to version 3 (which was currently referenced in the docs). This PR updates the list of ITU materials and their frequency ranges to align with version 4.

Summary of changes:

• Updated ITU materials & properties: Added new materials (clear_acrylic, vinyl_tile, carpet_tile, asphalt_concrete, and vacuum) and extended the existing frequency ranges up to 450 GHz in sionna.rt.radio_materials.itu according to Table 3 of ITU-R P.2040-4.
• Default material colors: Added default visual colors for the 4 newly introduced materials in ITURadioMaterial.ITU_MATERIAL_COLORS (leaving existing material colors untouched). I tried to pick nice colors, but feel free to give you opinion on these ;-)
• Documentation & Citations: Updated the BibTeX entry in rt.bib and refreshed all citation references (:cite:p:) across the codebase and docs to refer to P.2040-4.
• Auto-generated materials table: Added a custom Sphinx extension (itu-materials-table) that generates the materials table in radio_materials.rst directly from ITU_MATERIALS_PROPERTIES and ITU_MATERIAL_COLORS. The table includes grouped headers matching the previous layout as well as inline color swatches. I believe this is much easier to have this table be automatically generated, rather than having to kept both the table and the Python files in sync.

Let me know if you'd like any adjustments! :-)

See below for screenshots of Table 3 from the ITU recommendation.