fix: make csf::Peer::getTelemetry() static to satisfy clang-tidy

The test Peer adaptor's getTelemetry() returns a shared function-local
NullTelemetry instance and does not read any per-peer state, so
clang-tidy's readability-convert-member-functions-to-static flags it as
an error under -warnings-as-errors. Mark it static; it has no callers
that depend on it being a non-static member.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/test/csf/Peer.h

@@ -640,9 +640,10 @@ struct Peer
      *
      *  The test Peer adaptor uses a static disabled NullTelemetry instance
      *  so that all shouldTrace*() checks return false and no spans are
-     *  created during simulation tests.
+     *  created during simulation tests. It is static because the shared
+     *  disabled instance does not depend on any per-peer state.
      */
-    telemetry::Telemetry&
+    static telemetry::Telemetry&
     getTelemetry()
     {
         static auto tel = telemetry::makeTelemetry(