Add Hashable to Configuration & Consistency enums

[rnro]

There are a few simple public enums which I think it would be convenient if they were equatable, and if Equatable why not Hashable.

Motivation:

I think it would be useful if these simple enums e.g SpeculativeExecutionPolicy were Equatable to allow things like assertions to operate on them conveniently.

Modifications:

Add Hashable conformance to some simple enums.

• Configuration.SpeculativeExecutionPolicy
• Configuration.PrepareStrategy
• Consistency

Result:

More ergonomic comparison and use of enums.