Upgrade libsodium to 1.0.20

[GrahamCampbell]

Release Notes

• Building with zig build now requires Zig 0.12.
• When using the traditional build system, -O3 is used instead of -Ofast.
• Improved detection of the compiler flags required on aarch64.
• mproved compatibility with custom build systems on aarch64.
• apple-xcframework: VisionOS packages are not built if Xcode doesn't include that SDK.
• crypto_kdf_hkdf_sha512_statebytes() was added.
• When using Visual Studio, runtime CPU feature detection is now enabled on Windows/aarch64.
• There were issues with C++ guards affecting usage of libsodium using Swift on Windows. This has been fixed.
• Emscripten: crypto_aead_aegis*() functions are now exported in JavaScript builds
• Emscripten: unsupported --memory-init-file option has been removed.
• apple-xcframework: the minimal deployment target can be set to iOS 11+.
• .NET packages now include precompiled libraries for Windows/arm64, iOS, TvOS and Catalyst.
• .NET precompiled libraries now work on any CPUs, using only runtime feature detection.
• SYSV assembly should not be used when targeting Windows (reported by @meiyese, thanks!)
• Compatibility issues with LLVM 18 and AVX512 have been addressed.
• GitHub attestation build provenance are now added to NuGet packages.
• JavaScript tests can now use Bun as an alternative to Node.