feat(gateway): monotonic clock helper (1879)

tests/unit/connection/test_clock.py

@@ -0,0 +1,8 @@
+from ingestor.connection.clock import MonotonicClock
+
+
+def test_elapsed_is_non_negative_and_monotonic():
+    clk = MonotonicClock()
+    a = clk.elapsed()
+    b = clk.elapsed()
+    assert a >= 0 and b >= a  # never negative even if wall clock jumps back