refactor: why you so salty? Entirely remove libsodium from D++

[braindigitalis]

This PR completely removes libsodium as a dependency for voice in D++. No longer do we have to be all salty.
The replement uses OpenSSL primitives instead, plus a pair of functions i lifted from BoringSSL (due credit given) and converted from ugly macros to constexpr.

All build systems that look for and include/link sodium have been adjusted to remove it from the library. All documentation no longer refers to sodium. Note that we do keep previous verisons documentation which will still correctly refer to sodium for those versions.

Code change checklist

• I have ensured that all methods and functions are fully documented using doxygen style comments.
• My code follows the coding style guide.
• I tested that my change works before raising the PR.
• I have ensured that I did not break any existing API calls.
• I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

Note: GPT used to help explain what HChaCha20 actually is and its role in nonce expansion. Some of the comment docblocks have their origin from the evil AI.

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[Jaskowicz1]

Why so serious?

[braindigitalis]