Support `hint_min_samplerate`

[paulfd]

See #566, but find a way to make it cheap when not opting in; also link it with the plugin oversampling factor.

[PythonBlue]

Thanks for being willing to consider implementing my idea into the main fork. I realize my own implementation was extremely crude, no thanks to my failed attempts to update it, so if we can make it more efficient, programmatically and performance-wise, all the better.