Add validations for case names, dates, and download URLs in _sanity_check

[Luis-manzur]

This pull request introduces new validations to the _check_sanity method in AbstractSite to enhance data integrity checks and improve error handling.

Enhancements to _check_sanity validations:

• Added checks for suspicious file extensions in download_urls using a regular expression to detect potentially unsafe or unexpected file types.
• Introduced validation for forbidden characters in case_names, logging warnings when detected.
• Added a new sanity check to ensure case_dates are not earlier than the year 1900, raising an exception for invalid dates.

[flooie]

Looks like we added validation for url endings --- can we remove this please and focus just on the validation for dates

[flooie]

I think I would want to add more tests and do further research into the other components and I think it complicates this PR.