Constellations as species

[mantepse]

Provide constellations as (an example of) a combinatorial species.

Dependencies: #41534

[github-actions]

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[videlec]

Here is a test for transitivity without relying on graph connectedness (it does not handle the case of the symmetric group on the empty set)

def perms_are_transitive(sym, p):
    D = sym.domain()
    orbit = set()
    x0 = D.an_element()
    todo = [x0]
    orbit.add(x0)
    n = 1
    while todo and n < len(D):
        x = todo.pop()
        for pp in p:
            y = pp(x)
            if y not in orbit:
                todo.append(y)
                orbit.add(y)
                n += 1

    return n == len(D)

It is roughly 10x faster than what is in constellation.py.