Update `examples/webaudio` for 2025

[joeljaffesd]

Hi Marek,

I'm a university student working on a project of similar nature to cppsketch, in particular, the audioweb example.
When I build and serve the project for the web, I encounter the following issues:

1. When building, em++ complains about the -sEXTRA_EXPORTED_RUNTIME_METHODS=['cwrap', 'ccall'] flag, the modern equivalent is simply EXPORTED_RUNTIME_METHODS.
2. When serving, I get a deprecation warning regarding the use of ScriptProcessorNode rather than AudioWorklet, and the following error starts piling up at what seems to be the block rate:

Uncaught TypeError: Cannot read properties of undefined (reading 'buffer')
    at audioCallback (audio.js:47:49)
    at scriptNode.onaudioprocess (audio.js:100:3)

I've created a fork that handles the compilation flag, and am working towards solving the TypeError. My ultimate goal is to create a system that uses CodeMirror to allow for rapid iteration and testing of C++ audio code without a local dev env, something like the Faust Web IDE but for C++.

I would love to collaborate, should you have the time.