Improve sqlpp23-ddl2cpp custom types mapping

[rbock]

I have improved scripts/sqlpp23-ddl2cpp to better handle custom type mappings.

Key changes:

1. Arbitrary C++ Types: The --path-to-custom-types CSV mapping now supports any C++ type as a "base type". If the base type is not a built-in sqlpp type, the script creates a new parser for the associated SQL types.
2. Namespace Handling:
   • Unqualified C++ type names (e.g., integral, my_type) are now implicitly prefixed with ::sqlpp:: in the generated code.
   • Qualified C++ type names (e.g., boost::uuid, my_ns::my_type) are treated as custom types and used exactly as provided.
3. Consistent Annotations: This same logic applies to cpp_type annotations in the DDL, ensuring consistent behavior across all type override mechanisms.
4. Improved Parser Initialization: DdlParser.initialize now copies the built-in type lists before extending them, preventing side effects when the parser is re-initialized (which is common in unit tests).
5. Updated Tests:
   • scripts/sqlpp23-ddl2cpp-unit-tests now includes cases for qualified vs. unqualified types from both mappings and annotations.
   • Integration tests in tests/scripts/ have been updated with a new UUID SQL type mapping to my_ns::uuid to exercise the new functionality.

These changes provide more flexibility for users to map SQL types to their own C++ types while maintaining a clean and consistent naming convention for standard sqlpp types.

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PR created automatically by Jules for task 1074235339693974878 started by @rbock

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