fix(tracing): correct docstring for _now_ns helper

Remove misleading "monotonic" qualifier — time.time_ns() returns
wall-clock time, which is correct for OTel span timestamps.

Signed-off-by: Gary Atwal <garyatwalai@users.noreply.github.com>

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: garyatwalAI

nemoguardrails/tracing/governance_enricher.py

@@ -441,7 +441,7 @@ def _span_is_recording(span: Span) -> bool:
 
 
 def _now_ns() -> int:
-    """Return the current time in nanoseconds (monotonic wall clock)."""
+    """Return the current wall-clock time in nanoseconds."""
     return time.time_ns()