Return every possible input in place of solo op for exhaustive remove

in mutations.py in function check_every_remove_node, for solo operators return each possible input in place of 2 node tree. Right now, the same circuit is being appended to the final list for N number of inputs.

Open mutations.py and inspect check_every_remove_node, focusing on the solo-operator path and how circuits are appended to the final list. Reproduce the case with N inputs, then verify that the result contains each possible input instead of repeating the same 2-node tree.

Written by the indexing model from the issue text.