Added custom exception for indexers being treated as properties during serialization

[michelebastione]

Mirrors #884 on the maintenance branch

[gemini-code-assist]

Summary of Changes

Hello @michelebastione, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a dedicated exception to explicitly prevent the serialization of types that contain indexers. Previously, indexers might have been incorrectly processed as regular properties during serialization. By throwing MiniExcelNotSerializableException when an indexer is encountered, the change clarifies that such types are not serializable by default, providing better error handling and mirroring a fix from issue #884.

Highlights

• New Custom Exception: Introduced MiniExcelNotSerializableException to specifically handle cases where types cannot be serialized due to certain member types.
• Indexer Serialization Prevention: Modified the Property constructor to detect indexers and throw MiniExcelNotSerializableException, explicitly preventing types with indexers from being serialized as regular properties.
• New Test Case: Added TestIssue880_ShouldThrowNotSerializableException to validate that attempting to serialize a type containing an indexer correctly throws the new exception.

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[gemini-code-assist]

Code Review

This pull request introduces a new custom exception, MiniExcelNotSerializableException, to handle cases where types with indexers are attempted to be serialized. The logic to detect indexers and throw this exception is correctly implemented in the Property class constructor. A corresponding unit test has been added to verify this new behavior, ensuring that the correct exception is thrown. The changes are well-implemented and address the issue effectively. I have one suggestion to improve the new exception class by adhering more closely to .NET exception design guidelines.