Enhance Verification Constraints

This enhancement is requested by BAMT & EPDE users.
Rationale: some domains work a lot with custom constraints on valid solutions. Examples are EPDE and molecular search (drug design). Making them more usable and, possibly, effective, can facilitate general-purpose application of GOLEM.

The idea is that *intuitive & straightforward* general-purpose constraints on the search space is an important feature of GOLEM optimizer. So the issue is to make it better.

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Things to consider:
- We can have constraints on different stages of optimization:

- '**early**' constraints (that define search space before optimization, like graph depth or available nodes)
- '**intermediate**' constraints (that restrict which mutations can be applied and to which nodes; currently it's handled by optional `ChangeAdvisor`)
- '**late**' constraints (that are applied on mutated and evaluated graphs)

So, maybe it makes sense to somehow generalize this machinery behind one interface?

- Constraints can work on different representations of the graph & its properties

Sometimes constraints can be defined on matrix form of graph, sometimes on its spectral properties, sometimes on domain graph and sometimes on graph structure. We can consider a mechanism to get a required representation in verification rule.