------------------
- Refactoring `IntervalSet` to pure numpy ndarray.
- Implementing new chain of inheritance for time series with abstract base class. `base_class.Base` holds the temporal methods for all time series and `Ts`. `time_series.BaseTsd` inherit `Base` and implements the common methods for `Tsd`, `TsdFrame` and `Tsd`.
- Automatic conversion to numpy ndarray for all objects that are numpy-like (typically jax).