[WIP] Dual Time for NEMO solver + cleanups

[WallyMaier]

This PR addresses the dual-time solver of NEMO. A small lack of initialization of the solutions was causing problems.
There are also some small code clean-ups here and there.

Our current regression uses regular time-stepping, not sure if its worth adding an additional case for this.
I have yet to fully test this to make sure it works properly.

Related Work

#1391

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[WallyMaier]

closing and moving these changes to #1555