Deprecations via warnings don't work for Python libraries

Wild (and I guess most of the time bad) idea: on top of the warnings, introduce a `sleep` in the deprecated functions. At every version, increase the sleep.

Has this ever been considered?

The problem with warnings is that they're not really observable: few people actually read these logs, most of the time. Making the deprecation observable means annoying the library users. The question is then: what's the smallest annoyance we can come up with, so that they still have a look?

Yes, people do notice sleep. But it has to be on the scale of minutes or it will be ignored especially if it happens during a CI run.