crypto: unify validation of checkPrime checks

Previously, the JS layer would validate that the value of the checks option was an unsigned 32-bit integer, otherwise throwing an appropriate error but with a slightly misleading error message. Then the C++ layer would validate that the value was an unsigned 31-bit integer, otherwise throwing an appropriate error, but with a different (and even less helpful) error message.

Instead, make the JS layer aware of the 31-bit restriction so that no validation in C++ is necessary and so that the error message always matches the exact requirement.