Improve IdentityOperator and ScaledOperator actions

[albertomercurio]

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

I slightly improved the IdentityOperator and ScaledOperator action.

More specifically, I removed the update_coefficients in the IdentityOperator, as it is constant by construction.

I have also simplified the action of a ScaledOpertator. The previous implementation was directly using mul!, which I think it not always the case, as ScaledOperator may contain a more complex operator in L.L. So, I first update the coefficients of L.λ, and then directly apply the operator action L.L(w, v, u, p, t).

After merging this PR (if accepted), could we release a new version? It is needed to add support in QuantumToolbox.jl of the new v1 version.

[albertomercurio]

Could you release a new version of SciMLOperators.jl and SciMLBase.jl? We need it to support SciMLOperators.jl v1 in QuantumToolbox.jl

• CompatHelper: bump compat for SciMLOperators to 1, (keep existing compat) qutip/QuantumToolbox.jl#470