Update to Zig 0.14

[yoshibox]

Fix some files to build with Zig 0.14 (but can't be built with Zig 0.13 anymore)

There were some syntax errors that I didn't really understand but looking at past versions of the official documentation it seems that the syntax just changed:

Zig 0.13: https://ziglang.org/documentation/0.13.0/#toc-Inline-Switch-Prongs

const fields = @typeInfo(T).Struct.fields;

Zig 0.14: https://ziglang.org/documentation/0.14.0/#Inline-Switch-Prongs

const fields = @typeInfo(T).@"struct".fields;