Add increasing_substep_time_steppers list

[wthrowe]

Necessary property for worldtube particle tracking.

Not a huge fan of the name, so if anyone has a better idea feel free to suggest. Unfortunately, I've already used "monotonic" for a different property.

Proposed changes

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Further comments

[knelli2]

What is the other property that "monotonic" is used for? Is it really that bad if you use it again?

[wthrowe]

The AdamsMoultonPcMonotonic class and TimeStepper::monotonic() function refer to the "not deadlocking the control system" property.

[knelli2]

Hmm yeah probably shouldn't overload the meaning. However, it seems like using "monotonic" in this PR makes more sense and the other names should be changed to something else

[wthrowe]

Do you have a suggestion for the other one, then?

The two properties are, explicitly:

1. Time is non-decreasing for all operations (but substep times can repeat)
2. Substep time is strictly increasing (but things like dense-output time can decrease freely)

[knelli2]

Oh wow ok... Yeah I don't have a good idea how to differentiate these. They are so similar in many ways but just slightly different. I guess increasing_substep_time_steppers is ok for now.