Migrate to planus from flatc

[VirxEC]

Some syntax changes have been made.

• Unions have been collapsed into their parent, so no more .item

• The Float type no longer exists. PyFloat gets stored until .pack() is called, at which point the flat::Float is constructed automatically. This only applies to the state setting code where Float was used:

- dgs.match_info.game_speed.val += 1
+ dgs.match_info.game_speed += 1

- dgs.match_info.world_gravity_z = Float(-650)
+ dgs.match_info.world_gravity_z = -650

Non-forward facing changes:

Planus, a Rust implementation of the flatbuffers compiler with an emphasis on generating high-quality Rust code, is now used. The intermediate representation of the flatbuffers spec is used by the codegen script to generate the additional Python code, which is now ran through cargo fmt before being written to the disk.

The use of Planus's IR of the flatbuffers spec provides ergonomic access to all the data in a manor that's been heavily tested and verified against lots of inputs vs the old, custom sudo-parser.

[NicEastvillage]

Good changes 👍