feat(boot-test): test.yaml unboundPorts for ports opened only when a player connects

The first real run of the port check found that the crossplay Minecraft
server opens no UDP socket at startup: Bedrock goes through Geyser's
NetherNet transport, and 19132/udp is not open after boot. It is listed as
unboundPorts in that game's test.yaml, with the reason, until a Bedrock
client confirms how players reach it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

schema/test.schema.json

@@ -33,6 +33,11 @@
       "minimum": 10,
       "maximum": 3600
     },
+    "unboundPorts": {
+      "description": "Published ports the server only opens once a player connects, so the boot test doesn't expect them open. Each one exactly as in defaultPorts, with the reason in a comment.",
+      "type": "array",
+      "items": { "type": "string" }
+    },
     "holdSec": {
       "description": "How long the server must stay up after its ready line to pass (default 60). Its published ports are checked after it.",
       "type": "integer",