Improve ComposedScalarOperator update and concretization

[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

The previous implementation was inefficient and was allocating on more complex operators. I now use a generated function to help the compiler to handle this.

[albertomercurio]

Would it be possible to release a new version?

[ChrisRackauckas]

already done