fix: Replace device calls to memcpy with tu_memcpy_s

Introduces a new function tu_memcpy_s, which is effectively
a backport of memcpy_s. The change also refactors calls
to memcpy over to the more secure tu_memcpy_s.

src/class/dfu/dfu_rt_device.c

@@ -110,7 +110,7 @@ bool dfu_rtd_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_control_request
       TU_LOG2("  DFU RT Request: GETSTATUS\r\n");
       dfu_status_response_t resp;
       // Status = OK, Poll timeout is ignored during RT, State = APP_IDLE, IString = 0
-      memset(&resp, 0x00, sizeof(dfu_status_response_t));
+      TU_VERIFY(tu_memset_s(&resp, sizeof(resp), 0x00, sizeof(resp))==0);
       tud_control_xfer(rhport, request, &resp, sizeof(dfu_status_response_t));
     }
     break;