Implement correct iteration through disjoint enumerated set for infinite set

[user202729]

Previously, the iteration does not touch any finite set that comes after an infinite set.

This fixes the issue.

It tries to not change the existing behavior whenever all element sets are finite, by checking for finiteness.

Meanwhile fix a genuine bug in root_lattice_realizations where DisjointUnionEnumeratedSets([self.positive_real_roots(), self.positive_imaginary_roots()]) is returned, but both sets are infinite, so iterating through it will never reach any element in the second set.

📝 Checklist

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⌛ Dependencies

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