(maint) Remove unused OptionalAttributeOperation

The expression OptionalAttributeOperation was thought as an
instruction that would treat an assignment of :undef as
antimatter vs. setting an explicit nil. This is not possible
when using the 3x Resource class, and no concrete syntax was
introduced.

This removes it from the model and the todo note to implement it
in the evaluator.
(maint) Clean up stale comments
(maint) Remove unused constructs and use faster polymorph calls

This removes the ability to pass a block to evaluate since this
was only used in one specific case, and there are many calls to
evaluate (removes one conditional in very hot execution path).

Adds caching to polymorph tables in compare operator
sub evaluator.