[Feature Request]: Smoother API for .delete()

### Describe the problem

At the moment, there is no convenient way to delete all entries in a collection (without deleting the collection itself). Even though .delete() accepts `None` as an argument to `ids`, there is no "wildcard filter" that could be given to `where` as an argument.

### Describe the proposed solution

Either make .delete() delete all entries in the collection or make it possible to pass `where={}` as a wild-card filter matching all documents.

### Alternatives considered

_No response_

### Importance

would make my life easier

### Additional Information

_No response_

Start at the collection .delete() API and trace how ids=None and where filters are handled. Compare the two proposed behaviors, then inspect the existing deletion tests or test entry points in the repository. Done means one clearly chosen wildcard behavior deletes all entries without deleting the collection, with coverage for the new usage.

Written by the indexing model from the issue text.