Separate `EvaluationDetails` from `ResolutionDetails`

[toddbaert]

As mentioned here, these should be different objects. It's a minor issue, but the EvaluationDetails should be a subset of the EvaluationDetails, as mentioned here. There's no need for the provider to be setting the flag key when the SDK can do that.

See: https://openfeature.dev/specification/types/#resolution-details

Definition of Done:

• New ResolutionDetails type is added as per spec
• Provider interface updated to return this type

[mowies]

Hey @toddbaert , I'd like to work on this :)