[internal/otelarrow] [chore] fix TestMRUReset flakiness (open-telemet…

…ry#34260)

**Description:**

Ensure the monotonic clock has advanced prior to resetting, to ensure
the item generation is before the reset.
The monotonic clock is guaranteed to be non-decreasing, but may be
identical in consecutive measurements.

**Link to tracking Issue:**


open-telemetry#34252

**Testing:**

I couldn't reproduce the issue locally - this issue would depend on the
system clock frequency.

**Documentation:**

N/A

internal/otelarrow/compression/zstd/mru_test.go

@@ -6,6 +6,7 @@ package zstd
 import (
 	"runtime"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
 )
@@ -78,6 +79,9 @@ func TestMRUReset(t *testing.T) {
 	})
 	require.Equal(t, 1, m.Size())
 
+	// Ensure the monotonic clock has has advanced before resetting.
+	time.Sleep(10 * time.Millisecond)
+
 	m.Reset()
 	require.Equal(t, 0, m.Size())