feat(aws-ssm): add interface assertion to Provider

[gioddiggi]

This PR

Introduces a compile-time interface assertion to ensure that awsssm.Provider correctly implements theopenfeature.Provider interface.

✅ Benefits

• Provides compile-time safety and prevents accidental interface contract violations.

🔍 Example

If *awsssm.Provider stops implementing openfeature.Provider (e.g., due to a missing method), compilation will fail with a clear message:

*awsssm.Provider does not implement openfeature.Provider (missing SomeMethod method)