Breaking: merge instrument and rig, make rig accept components: List[Union[]]

[dbirman]

This PR merges the instrument.py and rig.py files together and sets up Rig to accept a List[Union[]] of components instead of specifying parameters to accept. Unfortunately it was best to do these together rather than separately, which makes this a very large PR.

To allow the Union to work properly the Assembly classes needed to have a device_type field added, even though they don't inherit from Device itself. The code throws warnings if you try to add a new option to the union that doesn't include the discriminator field, so there's no need to add a validator.

I discovered a huge number of tests that were mis-specified during this refactor, I've simplified testing so that instrument now properly tests its own validators (rather than being sprinkled in other files like test_imaging).

This PR got bloated... it now also:

• Deprecates platform