bug: auto-advertise on start

[vladopajic]

some streams are still open after test "auto-advertise on start" finishes, making all following tests to fail.

https://github.com/vacp2p/nim-libp2p/actions/runs/29260522802/job/86852254332

  [Test   ]           auto-advertise on start
INF 2026-07-13 15:13:10.885+00:00 Service Discovery started                  topics="service-discovery" tid=55127
INF 2026-07-13 15:13:10.887+00:00 Service Discovery started                  topics="service-discovery" tid=55127
WRN 2026-07-13 15:13:10.887+00:00 Starting kad-disco twice                   topics="service-discovery" tid=55127
WRN 2026-07-13 15:13:10.887+00:00 Starting kad-disco twice                   topics="service-discovery" tid=55127
INF 2026-07-13 15:13:10.894+00:00 Service Discovery started                  topics="service-discovery" tid=55127
WRN 2026-07-13 15:13:10.894+00:00 Starting kad-disco twice                   topics="service-discovery" tid=55127
=======================
  /Users/runner/work/nim-libp2p/nim-libp2p/tests/test_all 'Service Discovery Component - Advertise Discover::auto-advertise on start'
-----------------------
    Opened LPChannel: 3745
Closed LPChannel: 3744

  [FAILED ] (  0.07s) auto-advertise on start