Support for `uom`

[ElliotB256]

I would like to use the uom crate to define quantities in atomecs. https://github.com/iliekturtles/uom

Advantages:

• Compile-time dimensional analysis
• No runtime overhead
• Convenience to define in whatever unit is appropriate at the time
• No incorrect conversions

I had tried previously but was not able to because of the incompatibility of Vector3<> from nalgebra with uom. There have been a few updates to the package since then and it is worth revisiting.

[ElliotB256]

Switching to another ECS such as legion or bevy may solve this implicitly, as both define storage types different from specs.

[ElliotB256]

#3