support for specifying dynamic type lengths

[karmacoma]

/// @custom:halmos --array-lengths m=5
function test_dynamic_bytes(bytes memory m) {
   console.log(m.length);
}

I would have expected m.length to be 5, but it was 0x41 in my test.

The alternative is to use svm.createBytes(5, "m")

[karmacoma]

same issue for the string type