This commit refactors the AxisIterator and TimePlan classes in the example.py file. The changes include:
- Adding type hints and annotations to improve code readability and maintainability.
- Renaming the `length` method in AxisIterator to `num_timepoints` for clarity.
- Adding a new `deltas` method to TimePlan to iterate over the time deltas between timepoints.
- Handling the case of an infinite sequence in the `num_timepoints` method of TimePlan.

These changes improve the overall structure and functionality of the code.

…lues