Odd number for d_state

[Yaoyx]

Hi,

Thank you for this fascinating work.
I am still learning the whole concept. One question I have about DPLR and NPLR is that only half of conjugate pairs will be kept, then if we set d_state to an odd number, we will lose one state while reconstructing the matrix, as the code only multiplies the size by a factor of 2.

https://github.com/state-spaces/s4/blob/e757cef57d89e448c413de7325ed5601aceaac13/models/s4/s4.py#L1520C1-L1522C45

So I guess we should always assume d_state to be an even number?