Project serialization improvements

[Moneyl]

Moving some items from #34 here since they aren't required immediately to get the rewrite off the ground:

• [ ] Implement deserializer for Mat3 and Mat4 that only writes on of the union fields. Better for readability and manual editing.
• [ ] Change Mat3, Mat4, and Vec3 to write digits even if they're zero. Bon is writing ? for default values which I dislike.
• [ ] Move custom type serialize/deserialize functions to a static class + remove bon environment init to static constructor.
• [ ] Stop bon from allocating dummy objects when editor objects or project buffers are referenced during serialization.