refactor(metrics): drop never-passed get_metrics_output registry param (leanEthereum#977)

* refactor(metrics): drop never-passed get_metrics_output registry param

The Prometheus output helper accepted an optional collector registry
parameter that no caller ever passed.
Remove the dead parameter and export the default registry directly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* ci: re-trigger checks

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: tcoratger

src/lean_spec/node/metrics/registry.py

@@ -374,19 +374,14 @@ def reset(self) -> None:
 """
 
 
-def get_metrics_output(registry: CollectorRegistry | None = None) -> bytes:
+def get_metrics_output() -> bytes:
     """
     Serialize all registered metrics into Prometheus text exposition format.
 
     Typically called by an HTTP handler to serve the `/metrics` endpoint.
     The output is ready to return as a response body.
 
-    Args:
-        registry: Prometheus collector registry to export. Falls back to
-            the global default registry when not provided.
-
     Returns:
         UTF-8 encoded bytes in Prometheus text exposition format.
     """
-    reg = registry or REGISTRY
-    return generate_latest(reg)
+    return generate_latest(REGISTRY)