Fix LogFlusher unreachable 'no metrics' branch

Change condition from 'if parts:' to 'if len(parts) > 1:' to correctly
detect when no metrics are present beyond the prefix. Previously, parts
was always truthy since it was initialized with [self.__prefix], making
the 'No metrics to flush' message unreachable.

Author: cursoragent

sentry_streams/sentry_streams/metrics/metrics.py

@@ -189,7 +189,7 @@ def flush(
         for name, value, tags in gauges:
             tags_str = " ".join(tags) if tags else ""
             parts.append(f"gauge {name.value}={value} {tags_str}".strip())
-        if parts:
+        if len(parts) > 1:
             logger.info(" | ".join(parts))
         else:
             logger.info("No metrics to flush")