fix: Ensure we use casefold column name in raw data type map

[nj1973]

Description of changes

This PR fixes a bug where SQL Server CamelCase column names were bypassing raw data type checks.

I can't actually add the new test columns until after this PR is approved. I have manually tested but, after approval I'll add the columns and kick off a final test run before hitting merge.

I also documented a related SQL Server limitation.

Issues to be closed

Closes #1683

Checklist

• I have followed the CONTRIBUTING Guide.
• I have commented my code, particularly in hard-to-understand areas
• I have updated any relevant documentation to reflect my changes, if applicable
• I have added unit and/or integration tests relevant to my change as needed
• I have already checked locally that all unit tests and linting are passing (use the tests/local_check.sh script)
• I have manually executed end-to-end testing (E2E) with the affected databases/engines

[nj1973]

/gcbrun

[nj1973]

/gcbrun