Guard against N_steps != 1

[mrossinek]

The LayerwiseEvolver based on tenpy has a N_steps argument in its public evolve method.
However, also as documented, this is supposed to be 1.

When it is not set to 1, the code runs fine but produces unexpected results.
This PR adds a guard against this to ensure the user cannot run into this.

[mrossinek]

This is an ad-hoc fix. We should have a more general discussion on how to handle copyright headers in the Qiskit addons.

Here, I did what I also used to do back in the application modules (which is to ensure the year of the latest change of a file is present with at most 2 years being listed). However, this regex cannot enforce that pattern consistently. In the application modules we had a tool to check these headers. We could consider using something similar but rather than copying this tool everywhere I would rather do something similar to the extremal-python-dependencies tool and ship this separately (if we decide that this is needed).

[coveralls]

Pull Request Test Coverage Report for Build 12634638468

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 12634274884:	0.0%
Covered Lines:	579
Relevant Lines:	579

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💛 - Coveralls