Make Iterative KH padding invariant

[qh681248]

What's the problem?

Currently, unit tests do not pass when Iterative KH is set to be padding invariant and probabilistic = True but passes otherwise, investigate what is causing the unit tests to fail? (Might potentially be fixed by #983 )

How can we reproduce the issue?

Add Padding Invariant solver to Iterative KH class definition and rerun the unit test

Python version

3.13

Package version

0.4.0

Operating system

windows

Other packages

No response

Relevant log output

[gw265981]

Iterative KH implementation superseded by #977.