python: Allow querying route delays

Signed-off-by: gatecat <gatecat@ds0.me>

python/delay_vs_fanout.py

@@ -0,0 +1,10 @@
+with open("delay_vs_fanout.csv", "w") as f:
+    print("fanout,delay", file=f)
+    for net_name, net in ctx.nets:
+        if net.driver.cell is None:
+            continue
+        if net.driver.cell.type == "DCCA":
+            continue # ignore global clocks
+        for user in net.users:
+            print(f"{len(net.users)},{ctx.getNetinfoRouteDelay(net, user)}", file=f)
+