docs: fix Sphinx build warnings; define math macros; restore richards.cADR extension - #47

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, conda-incubator/setup-miniconda@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

warning libmamba Executing post-link script for package 'openmpi'.

warning libmamba [mesa-lavapipe-26.2.4-h1d927ee_0] The following files were already present in the environment: - share/drirc.d/00-mesa-defaults.conf

warning libmamba Executing post-link script for package 'ucc'.

warning libmamba Executing post-link script for package 'gdk-pixbuf'.

warning libmamba Executing post-link script for package 'ucx'.

warning libmamba Security Warning: This transaction includes executing package scripts (pre/post-link/unlink) if present. These scripts can contain arbitrary code. Please ensure you trust the package sources.

warning libmamba Failed to fetch shard https://conda.anaconda.org/conda-forge/noarch/0b959f3ba80dc8382c1d60b94964895d352c7b52e4984c07dfb9e2883c66bd19.msgpack.zst for package execnet: Transfer finalized, status: 502 [https://conda.anaconda.org/conda-forge/noarch/0b959f3ba80dc8382c1d60b94964895d352c7b52e4984c07dfb9e2883c66bd19.msgpack.zst] 155 bytes

'nodefaults' channel detected: will remove 'defaults' if added implicitly. In the future, 'nodefaults' to remove 'defaults' won't be supported. Please set 'conda-remove-defaults' = 'true' in setup-miniconda to remove this warning.

warning libmamba Security Warning: This transaction includes executing package scripts (pre/post-link/unlink) if present. These scripts can contain arbitrary code. Please ensure you trust the package sources.