Missing Post-Frame Update Speeds

[scottnuma]

• The Slippi spec now includes 5 different speeds in the post-frame update information (spec)
• They were added ~recently in version 3.5.0

Offset	Name	Type	Description	Added
0x35	Self-induced Air x Speed	float	Negative means left, Positive means right	3.5.0
0x39	Self-induced y Speed	float	Negative means down, Positive means up	3.5.0
0x3d	Attack-based x Speed	float	Negative means left, Positive means right	3.5.0
0x41	Attack-based y Speed	float	Negative means down, Positive means up	3.5.0
0x45	Self-induced Ground x Speed	float	Negative means left, Positive means right	3.5.0

• The Post object does not currently contain these speed fields.
• I'd like to open a PR to implement these new fields, but before doing so I want to get any needed context for adding new fields.