Fix output names of unsteady simulation

[rois1995]

Proposed Changes

It solves two main issues in unsteady simulations:
1- if the history file is not updated during the simulation (ex. setting inner_iter = 0) the time iteration is not updated in the file output names.
2- mesh file output does not have the time iteration at the end.

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[rois1995]

I would also try to add the writing of the mesh in the CGNS format, although this can be done in another PR.

[bigfooted]

LGTM