feat: validate provider services and fix logger injection

[aubes]

Provider services are now validated at compile time with clearer errors:

• The provider class must be set on the service itself. A provider created by a factory, or inheriting from a parent under an id that is not a class name, now needs an explicit class option (OpenFeature\interfaces\provider\Provider is accepted when the concrete class is unknown).
• A missing class now fails with an explicit "cannot be found" message, and a provider whose parent class or interface is missing reports that missing class.

Logger injection fixes:

• Providers now receive the application logger when MonologBundle is not installed; previously they got none.
• A logger already set on a provider service (e.g. a dedicated Monolog channel) is no longer overridden.