Fix running tests on individual crates

[branan]

Which part of the code is the issue addressing?

• Addressing a bug

Description

Being able to compile a given crate just for tests and/or benchmarks requires that a number of feature flags be properly passed along to the dependency crates. Not all of our crates do this correctly - instead, many only work when being built as a dependency of something like a full runtime, relying on the runtime to pass along the correct feature flags.

Research/based on

My own frustrations in attempting to run subsets of tests, only to find build errors.

How will this affect the code base

Cargo.toml files will have more explicit information about how feature flags should be propagated to dependencies. This is just more surface for diffs as dependencies change.

What are forseen obstacles or hurdles to overcome?

Maintaining this as Substrate updates and we add/remove dependencies is probably a fool's errand - we'll likely break it. Instead, we should always just aim to fix issues when we find them moving forward.