[Metrics] Scope unregister_vllm_metrics() to strictly "vllm:" metrics (vllm-project#42331)

`unregister_vllm_metrics()` currently uses "vllm" in `collector._name` to decide
which collectors to remove from the Prometheus registry, removing every even
metrics registered by other subsystems or downstream extensions like "vllm_omni:"

Signed-off-by: vraiti <vraiti@redhat.com>
Signed-off-by: Mark McLoughlin <markmc@redhat.com>

Author: vraiti

vllm/v1/metrics/prometheus.py

@@ -64,7 +64,7 @@ def unregister_vllm_metrics():
     registry = REGISTRY
     # Unregister any existing vLLM collectors
     for collector in list(registry._collector_to_names):
-        if hasattr(collector, "_name") and "vllm" in collector._name:
+        if hasattr(collector, "_name") and collector._name.startswith("vllm:"):
             registry.unregister(collector)