Cast from string to date with "/"

### Is your feature request related to a problem or challenge?

I want to be able to cast a string that is delimited with "/" to a date the same way that you can when it is delimited with "-". Postgres supports both.

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start by tracing DataFusion's string-to-date cast handling and its existing behavior for hyphen-delimited dates. Confirm that slash-delimited input is accepted consistently with PostgreSQL, and add or update regression coverage; done means the requested cast succeeds.

Written by the indexing model from the issue text.