Make sure the input rate and the output rates are same if the stream is duplex

[ChunMinChang]

The cubeb.c disallows to create a duplex stream with different input rates and output rates. However, it's ok to do so in this crate:

https://github.com/ChunMinChang/cubeb-coreaudio-rs/blob/dce7ddc846fb4784b4452f6eda282b67d286e27d/src/backend/tests/interfaces.rs#L487-L499

Aligning the policy here and the policy used in the main cubeb repo makes more sense and causes less confusion. Otherwise, the reader may have different assumptions when reading the code.

A good first step is to add an assertion when initializing the stream.