MAINT: Day.delta deprecation in pandas

[jklenzing]

Description

From running the unit tests:

  /home/runner/work/pysat/pysat/pysat/_orbits.py:382: FutureWarning: Day.delta is deprecated and will be removed in a future version. Use pd.Timedelta(obj) instead
    step = dt.timedelta(seconds=step.delta.total_seconds())

Potential impact

• FutureWarning, will probably take place with pandas 3.0 release (2024?)
• Needs to be replaced or version capped

Potential solution(s)

Update to pds.Timedelta notation. Simply replacing this for step.delta breaks the code quite a bit. More research is needed.

Alternatives

Rewrite this section.