Fix small errors, use IterativeSolver interface for IDMRG and remove unnecessary type requirements

[AFeuerpfeil]

In this PR I refactored the IDMRG interface to simplify overloading the update for specific MPO and MPS types

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[AFeuerpfeil]

@lkdvos
Is there a reason, why you use

# write in terms of MultilineMPS
function changebonds(
        ψ::InfiniteMPS, operator::InfiniteMPO, alg, envs = environments(ψ, operator)
    )
    ψ′, envs′ = changebonds(
        convert(MultilineMPS, ψ), convert(MultilineMPO, operator), alg, Multiline([envs])
    )
    return convert(InfiniteMPS, ψ′), envs
end

only for an InfiniteMPO and not also for an InfiniteMPOHamiltonian?
As far as I can tell both use the exact same algorithm, so one could switch to the Multiline case anyway.