[examples/raytrace-parallel] Replace Bash with Python for Windows compatibility

[jthemphill]

I wanted to get this example running on my Windows machine without fiddling with Powershell environment variables, so I just rewrote the shell scripts as Python scripts.

Since this example already requires you to have a Python3 installation, this PR makes the example work cross-platform without introducing a new dependency on Python3.

It looks like CI has some dependency on build.sh existing, so I just made it redirect to build.py. That may make any error messages look a bit less friendly in CI, since they'll be Python tracebacks😥 I'll let you decide if this is worth the tradeoff!

[daxpedda]

I would be fine with it since the server is already in Python. Though I dislike that we are using shell scripts or Python at all here.

Considering all this stuff needs nightly anyway, maybe we could use cargo scripts instead?

Though this LGTM, I'm not familiar with Python, so another maintainer should have a look at this.

[Liamolucko]

This also seems fine to me.

I think it'd make sense to do the same thing for the wasm-audio-worklet example as well, since it also uses multithreading and as a result needs a basically identical build script and Python server. The same goes for #3606 and #3607.

[daxpedda]

Thanks!

[Liamolucko]

wasm-audio-worklet's README should also be updated.

[jthemphill]

Almost all of this was merged in when you merged #3603, because I had rebased #3603 onto this branch. The only things left to merge in this PR now are the README changes. Sorry for not communicating this better😥

[daxpedda]

Again, apologies for messing up in #3606.
I rebased this on top of #3606, so all changes should be included now.