Implementation of suggestions arising from pmslavin's review

[OliverWoolland]

Discussion thread documenting suggested changes here: #9

Major changes:

• cmake fetches catch2 automatically
• read / write methods now go via nlohmann json to/from_json methods
• error messages have been centralised
• unordered_map has been used in place of map

Deferred:

• Using a type to streamline property value type checking (Consider implementing PropertyValue base class to define literal / reference property types #15)

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Copilot summary

This pull request introduces several improvements and refactorings to the RO-Crate C++ library. The most significant changes include the introduction of a centralized error handling mechanism, improved error messages, and a switch to using unordered maps for better performance. Additionally, the CMake configuration has been updated to use a newer version and to fetch Catch2 via FetchContent for testing. The serialization and deserialization logic for RO-Crate entities has also been refactored for clarity and robustness.

Error handling improvements:

• Introduced an ErrorCode enum and a centralized error_message function to standardize and clarify error messages throughout the codebase. All exceptions now use these error codes and message templates, often with std::format for dynamic values. [1] [2] [3] [4] [5] [6] [7]

Performance and data structure updates:

• Replaced std::map with std::unordered_map for entity and property storage to improve lookup performance in Properties and EntityRegister. [1] [2]

Serialization and deserialization refactor:

• Refactored the RO-Crate serialization and deserialization logic by introducing to_json and from_json functions, improving code clarity and separation of concerns. Error handling for file I/O and JSON parsing is now more robust and uses the new error handling system. [1] [2]

Build system improvements:

• Updated the minimum required CMake version to 3.24 and switched Catch2 integration from find_package to FetchContent, ensuring consistent and up-to-date dependency management for tests. [1] [2]

These changes collectively improve maintainability, reliability, and performance of the RO-Crate library.