Add warning about sampling rate when using ShiftFrequency and SetFrequency in pulse schedules

[DanPuzzuoli]

An issue arose here when SetFrequency and ShiftFrequency were used to shift a channel frequency well away from what was specified in the channel_carrier_freqs argument to Solver.

The specified channel frequency couldn't be represented digitally with the given dt, and the simulations therefore produced strange results.

@nkanazawa1989 suggested raising a warning in the schedule interpretation step when the difference between the schedule frequency and the channel_carrier_freqs frequency is larger than the Nyquist frequency (and therefore can't be accurately represented). One minor technical issue with adding this is that this code can be compiled with JAX, so we'll need to take some technical care with handling this.