Update to Zig 0.17.0

[AnErrupTion]

See #220. The multi-threading example needs to be fixed.

[AnErrupTion]

Well, I'm stupid. I did not see this comment at the beginning of the file:

//! The additional header must be passed to the build using \`-Dlua_user_h=examples/user.h\`

So now it does work, haha. However, it was quite slow due to the allocator, and using the SmpAllocator fixes that issue.

[robbielyman]

It’s probably fine for the examples to be slow; they’re somewhere between tests and model code.

[AnErrupTion]

It’s probably fine for the examples to be slow; they’re somewhere between tests and model code.

Sure but, as a bonus, the SmpAllocator is guaranteed to be threadsafe, compared to whatever GPA Zig decided to initialise in std.process.Init.