feat: pass Decodable struct to flag evaluation (cont'd)

[fabriziodemaria]

Following up the work from #191

Changes

• Address the open question from the original PR: how to handle mismatches between the default value and the remote value.
  • Following the most common approach in the industry, we never merge values: either all the non-optional fields are populated from remote or the default value is returned as-is.
• Add OpenFeature compatibility for object evaluations

Detailed resolve behaviour

• More fields in the remote value are allowed and discarded
• More fields in the default value are not allowed and the entire resolve is default value
• Any type mismatch on the same field is not allowed and the entire resolve is default value

More nuances:

• Optional fields in the default value don't need to be in the remote value
• Nulls fields in the remote value should be mapped to default values fields (currently broken, the entire resolve is default value)

Gotchas

• Date and DateComponents are returned as String, and should be defined as String in the passed in Codable T