Generalize LTS communication handling

[wthrowe]

The old version made assumptions based on the Adams-Bashforth method, but that won't be true for other methods.

Proposed changes

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Further comments

[knelli2]

Should we maybe say what the arbitrary decision is? Just that for the arbitrary case, we check which step size is smaller?

[wthrowe]

It's not that simple. That's just the last tie-breaker. The part of the algorithm that does the meaningful ordering also distinguishes some arbitrary cases.