Introduced `StaticReCClientTests` to validate the behavior of
the `ReCClient` static client, ensuring deterministic and
non-parallel execution due to process-wide state mutation.
Added tests to cover various scenarios:
- Null configuration callback throws `ArgumentNullException`.
- Missing `BaseAddress` or `ConfigureClient` throws.
- Conflicting `BaseAddress` and `ConfigureClient` throws.
- Successful static client build and resolution via `Create`.
- Subsequent `BuildStaticClient` calls throw exceptions.
Included helper types for `ConfigureServices` validation and
used `#pragma` directives to suppress warnings for obsolete
members. Ensured test order with `[Order]` attributes.
