Update Unity3D Native Plugin

I have the full source of a Unity3D native plugin that currently builds and runs on Windows and on Intel-based macOS. What I need now is a clean rebuild that still runs on those two targets — but also ships a native build for Apple Silicon, all while upgrading the embedded Opus dependency from version 1.1.2 to 1.5.2.

The code itself is untouched since the last release, so the work is almost entirely about modernising the Xcode / Visual Studio project files, adjusting any pre-processor flags, bringing in the newer Opus sources, and producing the three final binaries. All existing functionality must stay intact; no feature regressions are acceptable.

I don’t have pre-configured test machines for any of the platforms, so I will rely on your guidance for practical smoke tests or example scenes that prove each build works inside Unity.

Deliverables (all three must be produced):
• Compiled, ready-to-drop-in plugin binaries for Windows, macOS (Intel and Apple Silicon, likely in the same .bundle)
• Updated project/solution files and build scripts showing exactly how you generated each binary
• Brief build & integration notes so I can reproduce the process on my end

If you’ve handled multi-arch Unity plugins before, this should be pretty easy.