Add Support for Virtual Columns and Improve Error Messages in URL Table Function

Why it matters

This feature allows users to access metadata about the source files when querying data via the url table function, enhancing query capabilities and debugging by exposing the originating file and path. Additionally, clearer error messages help users more easily identify and resolve issues when using the url table function.

How to use it

When using the url table function in a SELECT statement, users can now reference the virtual columns _file and _path to retrieve the filename and full path of the fetched data respectively. Improved error messages will automatically be shown when problems occur.