fix: ruff warnings

docs/module/metrics.md

@@ -47,10 +47,12 @@ If neither of these applies to you, declaring metrics at module level (e.g. `HTT
 ```python
 from prometheus_client import Counter, Histogram
 
+
 @metrics.register
 def http_requests():
     return Counter("http_requests_total", "Total HTTP requests", ["method", "status"])
 
+
 @metrics.register
 def request_duration():
     return Histogram("request_duration_seconds", "Request duration")
@@ -79,6 +81,7 @@ from prometheus_client import Gauge
 
 _queue_depth = Gauge("queue_depth", "Current queue depth")
 
+
 @metrics.register(collect=True)
 def collect_queue_depth():
     _queue_depth.set(get_current_queue_depth())