feat: add phases to TimePlanWidget

[fdrgsp]

This PR adds to the TimePlanWidget the possibility to set useq-schema MultiPhaseTimePlan.

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[codecov]

Codecov Report

Patch coverage: 97.76% and project coverage change: +0.08 🎉

Comparison is base (2ebadea) 89.50% compared to head (789682b) 89.59%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #132      +/-   ##
==========================================
+ Coverage   89.50%   89.59%   +0.08%     
==========================================
  Files          37       37              
  Lines        4918     4977      +59     
==========================================
+ Hits         4402     4459      +57     
- Misses        516      518       +2     

Impacted Files	Coverage Δ
src/pymmcore_widgets/_mda/_time_plan_widget.py	97.05% <96.90%> (+3.58%)	⬆️
src/pymmcore_widgets/_mda/_mda_widget.py	93.44% <100.00%> (-0.04%)	⬇️
src/pymmcore_widgets/_util.py	75.34% <100.00%> (-0.10%)	⬇️

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[tlambert03]

Pint can do all those unit conversions for you, see https://pyapp-kit.github.io/superqt/widgets/qquantity/

And pint quantity: https://pint.readthedocs.io/en/0.7.2/tutorial.html

So you shouldn't need timedelta_to_units ..,