tor-proto: Replace sleep() in test with advance_until_stalled().

This test spuriously failed on my !2720 (merged) branch (https://gitlab.torproject.org/gabi-250/arti/-/jobs/811495):

failures:
---- circuit::test::invalid_circ_sendme stdout ----
E tor_proto::channel::reactor: UniqId(71): Running reactor
E tor_proto::circuit::reactor: Circ 23.17: Running circuit reactor
E tor_proto::circuit::reactor: Circ 23.17: reactor received AddFakeHop { relay_cell_format: V0, fwd_lasthop: false, rev_lasthop: false, params: CircParameters { extend_by_ed25519_id: true, ccontrol: CongestionControlParams { alg: FixedWindow(FixedWindowParams { circ_window_start: 1000, circ_window_min: 100, circ_window_max: 1000 }), cwnd_params: CongestionWindowParams { cwnd_init: 124, cwnd_inc_pct_ss: Percentage { value: 100 }, cwnd_inc: 1, cwnd_inc_rate: 31, cwnd_min: 124, cwnd_max: 4294967295, sendme_inc: 31 }, rtt_params: RoundTripEstimatorParams { ewma_cwnd_pct: Percentage { value: 50 }, ewma_max: 10, ewma_ss_max: 2, rtt_reset_pct: Percentage { value: 100 } } } }, done: Sender { complete: false } }
E tor_proto::circuit::reactor: Circ 23.17: reactor received AddFakeHop { relay_cell_format: V0, fwd_lasthop: true, rev_lasthop: true, params: CircParameters { extend_by_ed25519_id: true, ccontrol: CongestionControlParams { alg: FixedWindow(FixedWindowParams { circ_window_start: 1000, circ_window_min: 100, circ_window_max: 1000 }), cwnd_params: CongestionWindowParams { cwnd_init: 124, cwnd_inc_pct_ss: Percentage { value: 100 }, cwnd_inc: 1, cwnd_inc_rate: 31, cwnd_min: 124, cwnd_max: 4294967295, sendme_inc: 31 }, rtt_params: RoundTripEstimatorParams { ewma_cwnd_pct: Percentage { value: 50 }, ewma_max: 10, ewma_ss_max: 2, rtt_reset_pct: Percentage { value: 100 } } } }, done: Sender { complete: false } }
E tor_proto::circuit::reactor: Circ 23.17: reactor received BeginStream { hop_num: HopNum(2), message: Begin(Begin { addr: [119, 119, 119, 46, 101, 120, 97, 109, 112, 108, 101, 46, 99, 111, 109], port: 443, flags: BeginFlags(IPV6_OKAY) }), sender: Sender { tx: Sender { closed: false }, mq: TypedParticipation(Participation(Noop)) }, rx: Receiver { inner: ReceiverInner { state: Mutex { data: Ok(ReceiverState { rx: StreamUnobtrusivePeeker { buffered: None, poll_waker: None, inner: Some(Receiver { closed: false }) }, mq: TypedParticipation(Participation(Noop)), collapse_callbacks: 0 }), poisoned: false, .. } } }, done: Sender { complete: false }, cmd_checker: DataCmdChecker { expecting_connected: true } }
  Using RNG seed ARTI_TEST_PRNG=62d085c0fb1213c4f41d1a0a5c3f92dd10223a27c42bfda3caedfe60e011e95d
E tor_proto::circuit::reactor: Circ 23.17: handling cell: Relay(Relay { body: .. })
  Using RNG seed ARTI_TEST_PRNG=fd2f2f045a7340f1189972b13645346943efa2c42f43afd2161420c692bb4ff0
E tor_proto::circuit::reactor: Circ 23.17: handling cell: Relay(Relay { body: .. })
E tor_proto::circuit::reactor: Circ 23.17: Circuit reactor stopped: Err(CircProto("Mismatched tag on circuit SENDME"))
E tor_proto::channel::reactor: UniqId(71): reactor received CloseCircuit(CircId(128))
E tor_proto::channel::reactor: UniqId(71): Circuit 128 is gone; sending DESTROY
thread 'circuit::test::invalid_circ_sendme' panicked at crates/tor-proto/src/circuit.rs:2262:21:
reactor continued running after invalid sendme
failures:
    circuit::test::invalid_circ_sendme
test result: FAILED. 142 passed; 1 failed; 1 ignored; 0 measured; 0 filtered out; finished in 4.93s

This is probably because of the sleep()-based check. This branch changes the test to use MockRuntime, replacing the sleep() with advance_until_stalled().