Reproducibility for `OrdinalPatternEncoding`

[kahaaga]

Currently, the isless_rand function, which we use as the default value comparator for OrdinalPatternEncoding, will not give reproducible results. This is because we don't provide an rng argument to the rand call.

To solve this, we could either:

• Force the user to provide their custom lt function, taking care of reproducibility themselves (not preferable IMHO)
• Include rng as a field to both OrdinalPatternEncoding and OrdinalPatterns, which gets passed on to isless_rand.

Or maybe there's a better way?