Moved static provider logic to a new partial class `ReCClient.Static.cs` to support legacy scenarios (e.g., .NET Framework) without requiring an external `IServiceProvider`.
Introduced new static methods for building and resolving a static `IServiceProvider`:
- `BuildStaticClient(Action<StaticBuildConfiguration>)`
- Overloads for simpler configuration with `apiUri` or `HttpClient`.
Marked static methods as `[Obsolete]` to discourage use in modern DI-based applications.
Refactored `ReCClient` to focus solely on instance-level functionality, improving code organization and maintainability. Added documentation to clarify the intended use of static methods.
