fixes evmos#640

simulations are very basic: they can be built and executed,
but they don't generate any EVM-related transactions yet.
(It should be a matter of adding simulation-related code to the
modules + potentially extra helpers to the simulation.)
handler tests miss some extra assertions due to changes
in the return values snapshotting logic (ADR-001 and ADR-002).

Besides the test suites identified in the audit,
there's also "importer_test.go" which wasn't yet fixed.
(it'd require major rewriting + extra test resources)