feat: add port-name-padding parameter

Replaces the hard-coded 2pt padding used when placing port name labels.
Configurable per element via port-name-padding on elmt (forwarded by
block and group), defaulting to 2pt to preserve existing layout.

gallery/test_group_ports.typ

@@ -6,7 +6,7 @@
 #set page(width: auto, height: auto, margin: .5cm)
 
 #circuit({
-  // --- Group with port labels OUTSIDE (default) ---
+  // --- Group with port labels INSIDE (outside-port-names: false) ---
   element.group(
     id: "cpu",
     name: "CPU (labels outside)",
@@ -14,6 +14,7 @@
     stroke: (dash: "dashed"),
     fill: util.colors.yellow.lighten(60%),
     padding: 1em,
+    port-name-padding: .5em,
     outside-port-names: true,
     ports: (
       west: (
@@ -51,6 +52,7 @@
     fill: util.colors.yellow.lighten(60%),
     padding: 4em,
     outside-port-names: false,
+    port-name-padding: 0.5em,
     ports: (
       west: (
         (id: "in1", name: "D1"),