Reimplement opt_share to work on $alu and $pmux

tests/opt/opt_share_cat.ys

@@ -1,9 +1,13 @@
 read_verilog opt_share_cat.v
-prep -flatten
-opt
-pmuxtree
-opt_share
-opt_clean
+proc;;
+copy opt_share_test merged
 
-select -assert-count 2 t:$sub
-select -assert-count 0 t:$add
+alumacc merged
+opt merged
+opt_share merged
+opt_clean merged
+
+miter -equiv -flatten -ignore_gold_x -make_outputs -make_outcmp opt_share_test merged miter
+sat -set-def-inputs -verify -prove trigger 0 -show-inputs -show-outputs miter
+
+select -assert-count 2 -module merged t:$alu