autoname: avoid O(iterations x module size) full rescan

AutonamePass rescanned every selected cell/wire from scratch on every
iteration, and naming only propagates one hop per iteration, so cost
scaled with O(iterations x module_size). On a large, fully flattened
netlist with long dependency chains this meant multi-hour runtime and
40+ GB RSS. Likely the same issue as #5394, #4509 and #2816.

Replace the full-rescan loop with a ModuleAutonamer that keeps a
persistent worklist and only recomputes an object's proposal when a
direct neighbor was just renamed, using precomputed adjacency. Same
round-by-round batching as before, so the final naming is unchanged.

Adds tests/various/autoname_scaling.sh, which checks a 10000-cell
propagation chain still autonames within a time budget the old
algorithm could not meet.

tests/various/autoname_scaling.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+# Regression test for the incremental worklist rewrite of autoname_worker
+# ("autoname: avoid O(iterations x module size) full rescan").
+#
+# Before that change, AutonamePass::execute() rescanned every selected
+# cell's every connection on every round. Naming only propagates one hop
+# per round, so a design containing a long public-name-to-public-name
+# propagation chain of length N needed O(N) rounds, each doing an O(N)
+# rescan: O(N^2) total. This builds such a chain and checks that autoname
+# finishes within a time budget the old O(N^2) algorithm could not meet
+# (it took tens of seconds at this size; the fixed algorithm takes low
+# single-digit seconds), without pinning an exact runtime, which would be
+# too flaky across machines.
+
+set -e
+
+if ! which timeout > /dev/null; then
+    echo "No 'timeout', skipping test"
+    exit 0
+fi
+
+n=10000
+il=autoname_scaling.il
+trap 'rm -f $il' EXIT
+
+{
+    echo 'module \top'
+    echo '  wire input 1 \a'
+    for i in $(seq 0 $((n-1))); do
+        echo "  wire \$w$i"
+    done
+    prev='\a'
+    for i in $(seq 0 $((n-1))); do
+        echo "  cell \$not \$c$i"
+        echo '    parameter \A_SIGNED 0'
+        echo '    parameter \A_WIDTH 1'
+        echo '    parameter \Y_WIDTH 1'
+        echo "    connect \\A $prev"
+        echo "    connect \\Y \$w$i"
+        echo '  end'
+        prev="\$w$i"
+    done
+    echo 'end'
+} > $il
+
+if ! timeout 20 ${YOSYS} -q -p "read_rtlil $il; autoname" ; then
+    echo "autoname did not finish a $n-long propagation chain within the time" \
+         "budget -- looks like the O(iterations x module size) full-rescan" \
+         "behaviour is back"
+    exit 1
+fi