Improve experience developing on this project with rust-analyzer

[nspin]

At the time of writing, rust-analyzer imposes a one-configuration-fits-all approach to each workspace. This is incompatible with this project. We have some crates that only make sense on the development machine, and some that only make sense on seL4 or bare-metal.

We need to come up with a way to dynamically apply rust-analyzer to different configurations.

An acceptable intermediate solution would be preventing rust-analyzer from analyzing crates that don't make sense in the context of some default configuration. As far as I can tell, at present, that is not possible.