test: preserve event timestamp precision

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot-Session: bf00a0ac-e11f-4015-b295-3cdd9b491229

Author: AchoArnold

tests/read_receipts_test.go

@@ -134,7 +134,7 @@ func TestMessageThreadReadReceipts(t *testing.T) {
 			"content":   "Unread inbound message",
 			"encrypted": false,
 			"sim":       "SIM1",
-			"timestamp": time.Now().UTC().Format(time.RFC3339),
+			"timestamp": time.Now().UTC().Format(time.RFC3339Nano),
 		},
 		http.StatusOK,
 		nil,
@@ -161,7 +161,7 @@ func TestMessageThreadReadReceipts(t *testing.T) {
 			"from":      contact,
 			"to":        phone.PhoneNumber,
 			"sim":       "SIM1",
-			"timestamp": time.Now().UTC().Format(time.RFC3339),
+			"timestamp": time.Now().UTC().Format(time.RFC3339Nano),
 		},
 		http.StatusOK,
 		nil,