test: enhance LazyReflectionConverterTests with serialization and filtering scenarios

[IvanMurzak]

This pull request refactors the LazyReflectionConverter and its related tests to improve how property and field serialization is delegated and filtered, especially when using a backing converter. The changes ensure that ignored properties and fields are consistently respected, and that the converter works correctly even when a backing converter is present. The test suite is expanded to cover these scenarios and verify correct behavior.

Converter logic improvements

• Refactored LazyReflectionConverter to delegate property and field serialization to the backing converter when present, using new GetSerializablePropertiesInternal and GetSerializableFieldsInternal overrides, ensuring correct filtering and delegation.
• Updated logic for collecting ignored properties and fields so that both base and instance-level ignored members are combined, ensuring all relevant members are filtered out during serialization.

Test enhancements

• Added new tests in LazyReflectionConverterTests to verify that ignored properties are correctly filtered even when a backing converter is used, and that constructing a converter with both a backing converter and ignored members no longer throws exceptions.
• Updated the test mock converter to track metadata access rather than method calls, aligning with the new delegation approach and ensuring assertions check for correct metadata access.

Minor code maintenance

• Adjusted the order of property filtering in BaseReflectionConverter to ensure obsolete properties are filtered after checking readability, improving clarity and correctness.
• Cleaned up unused imports in LazyReflectionConverter.cs.
• Simplified internal access to the target type by removing an unnecessary method.

[github-actions]

Test Results

    2 files      2 suites   8m 23s ⏱️
1 155 tests 1 155 ✅ 0 💤 0 ❌
2 310 runs  2 310 ✅ 0 💤 0 ❌

Results for commit 064b2c8.