Consider supporting Foundry's invariant testing

Based on a post-workshop EthCC question @JuanCoRo got asked; will move it to backlog for now.

We might consider supporting Foundry's invariant tests, which executes function call sequences in an attempt to break an invariant specified as a function, e.g.,

function invariant_job1() public {
   assertInvariants();
}

function invariant_job2() public {
   assertInvariants();
}

function assertInvariants() internal {
   assertEq(val1, val2);
   assertEq(val3, val4);
}

That is something we could do using symbolic execution (modulo path and configuration explosion).

Start with the linked Foundry invariant-testing documentation and the issue's Solidity examples. Compare the described function-call sequences and invariant functions with Kontrol's symbolic-execution capabilities, then determine the configuration and path-explosion constraints. Done means Kontrol can support the proposed invariant-testing workflow with documented behavior and coverage.