[NumLib] use piecewise linear interpolation for multipliers of iteration based time stepping scheme

Fixes: #3539 (closed)

Mild improvement can be achieved for the given benchmark case:

info: The whole computation of the time stepping took 4155 steps, in which
         the accepted steps are 4154, and the rejected steps are 1.

Vs previous/default constant interpolation:

info: The whole computation of the time stepping took 4165 steps, in which
         the accepted steps are 4163, and the rejected steps are 2.

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2. Tests covering your feature were added?
3. Any new feature or behaviour change was documented?