approx_distinct can't handle null, date and timestamp types

[killme2008]

Describe the bug

For example:

SELECT APPROX_DISTINCT(NULL);
SELECT APPROX_DISTINCT('2025-09-17'::DATE);
SELECT APPROX_DISTINCT('2025-09-17 16:36:00'::TIMESTAMP);

All of these queries fail with:

This feature is not implemented: Support for 'approx_distinct' for data type xxx is not implemented

However, they should be supported for the sake of functional completeness.

To Reproduce

No response

Expected behavior

No response

Additional context

No response