add checks to `verifyDeadlock` and `verifyReach`

[jvoigtlaender]

In particular, the relevant instance types here contain fields minLength, withLengthHint, and rejectSpaceballsLength.

These should be checked "against each other", but also against the lengths of the sequences given in the instances.

The "checks against each other" can be inspired by checks already being done in the relevant config checkers.