minimize_space breaks runnability for patterns that are inconsistent with their graph flow #157
Description
Describe the bug
If a pattern has a graph with a flow but is not consistent with this flow, minimize_space leads to a pattern with is not runnable anymore.
To Reproduce
import graphix
pattern = graphix.pattern.Pattern(input_nodes=[0])
pattern.add(["N", 1])
pattern.add(["N", 2])
pattern.add(["E", (0, 1)])
pattern.add(["E", (1, 2)])
pattern.add(["M", 1, "XY", 0, [], []])
pattern.add(["M", 0, "XY", 0, [1], []])
pattern.add(["Z", 2, [0]])
pattern.simulate_pattern() # OK
pattern.minimize_space()
pattern.simulate_pattern() # KeyError: 1
Expected behavior
minimize_space should preserve pattern runnability.