Unwrap panic on SimpleReplace

[aborgna-q]

While trying to replace the two nodes in the middle of this diagram

graph LR
    subgraph 0 ["(0) DFG"]
        direction LR
        1["(1) Input"]
        2["(2) Output"]
        3["(3) MakeTuple"]
        4["(4) UnpackTuple"]
        1--"0:0<br>[]+[]"-->3
        1--"1:1<br>[]+[]"-->3
        3--"0:0<br>[[]+[], []+[]]"-->4
        3--"0:2<br>[[]+[], []+[]]"-->2
        4--"0:0<br>[]+[]"-->2
        4--"1:1<br>[]+[]"-->2
    end

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with this graph

graph LR
    subgraph 0 ["(0) DFG"]
        direction LR
        1["(1) Input"]
        2["(2) Output"]
        3["(3) MakeTuple"]
        1--"0:0<br>[]+[]"-->3
        1--"0:0<br>[]+[]"-->2
        1--"1:1<br>[]+[]"-->3
        1--"1:1<br>[]+[]"-->2
        3--"0:2<br>[[]+[], []+[]]"-->2
    end

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I got an unwrap panic on SimpleReplacement::apply:158

I wrote a pure-hugr failing test in

hugr/hugr-core/src/hugr/rewrite/simple_replace.rs

Lines 720 to 721 in 4e0ad64

	fn test_half_nots(
	dfg_hugr_half_not_bools: (Hugr, Vec<Node>),