feat(core): Introduce Graph Invariant checks

[brockelmore]

This introduces is_representation_ok which iterates through the graph ensuring that each context and its variables satisfy a set of invariants. The current invariants are basically placeholders.

It also introduces the ability to do inline test commands in solidity of the form:

contract A {
    function a(uint24 y) public pure {
        "pyro::variable::y::range::[0, 16777216]";
    }
}

This would perform a check that the variable y in this context has the provided range. Available test commands currently:

1. Variable
   • "range"
     • "pyro::variable::::range::[min,max]"
2. Coverage
   • "unreachable"
     - "pyro::coverage::unreachable"
   • "onlyPath" (this context should have no siblings - note: if you have a nested if statement (i.e. if (x ? y : false) {...}) it breaks)
     - "pyro::coverage::onlyPath"
3. Constraint
   • "constraint" - ensures the context has a constraint with the name provided
     - "pyro::constraint::(x != 0)"

Supercedes #85