Degeneralization keeps track of levels.

* NEWS: Document this.
* spot/twa/twagraph.cc: `copy_state_names_from` handles this new info.
* spot/twaalgos/degen.hh, spot/twaalgos/degen.cc: Implement it.
* tests/python/origstate.py, tests/python/simstate.py: Update tests to
  reflect the change.

tests/python/simstate.py

@@ -117,51 +117,51 @@ acc-name: parity min odd 4
 Acceptance: 4 Fin(0) & (Inf(1) | (Fin(2) & Inf(3)))
 properties: trans-labels explicit-labels trans-acc deterministic
 --BODY--
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-State: 2 "{₀[1]₀}"
+State: 2 "{₀[1#1]₀}"
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-State: 3 "{₀[0,0]{₁[1]₁}₀}"
+State: 3 "{₀[0#0,0#1]{₁[1#0]₁}₀}"
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+State: 4 "{₀[0#0,0#1] [1#1]{₁[1#0]₁}₀}"
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-State: 5 "{₀[1]₀}"
+State: 5 "{₀[1#0]₀}"
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+State: 6 "{₀[1#1]{₁[0#0,0#1] [1#0]₁}₀}"
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+State: 7 "{₀[1#1]{₁[0#0,0#1]₁}₀}"
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+State: 10 "{₀[0#0,0#1]{₁[1#1]₁}₀}"
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-State: 11 "{₀[1]{₁[0,0]{₂[1]₂}₁}₀}"
+State: 11 "{₀[1#1]{₁[0#0,0#1]{₂[1#0]₂}₁}₀}"
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