bug: panicked at 'supplied instant is later than self' on c6g.2xlarge EC2 (arm64)

[BugenZhao]

Thanks for your hard work on this excellent crate! Here is a bug report: when I was using it on an EC2 with arm64 architecture (c6g.2xlarge), I encountered 'supplied instant is later than self' frequently. Below is the backtrace.

Looks like the elapsed directly unwraps the checked_duration_since and panics on time going backward. However, the Instant from the standard library says,

Previous rust versions panicked when self was earlier than the current time. Currently this method returns a Duration of zero in that case. Future versions may reintroduce the panic.

What about also conforming to the behavior of std, so that there'll be no need to call now().saturating_duration_since(start_time)?

thread 'tokio-runtime-worker' panicked at 'supplied instant is later than self', /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/minstant-0.1.1/src/instant.rs:49:9
stack backtrace:
   0: rust_begin_unwind
             at ./rustc/9067d5277d10f0f32a49ec9c125a33828e26a32b/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at ./rustc/9067d5277d10f0f32a49ec9c125a33828e26a32b/library/core/src/panicking.rs:142:14
   2: core::panicking::panic_display
             at ./rustc/9067d5277d10f0f32a49ec9c125a33828e26a32b/library/core/src/panicking.rs:72:5
   3: core::panicking::panic_str
             at ./rustc/9067d5277d10f0f32a49ec9c125a33828e26a32b/library/core/src/panicking.rs:56:5
   4: core::option::expect_failed
             at ./rustc/9067d5277d10f0f32a49ec9c125a33828e26a32b/library/core/src/option.rs:1874:5
   5: core::option::Option<T>::expect
             at ./home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/minstant-0.1.1/src/instant.rs:49:9
   6: minstant::instant::Instant::duration_since
             at ./home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/minstant-0.1.1/src/instant.rs:49:9
   7: <minstant::instant::Instant as core::ops::arith::Sub>::sub
             at ./home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/minstant-0.1.1/src/instant.rs:205:9
   8: minstant::instant::Instant::elapsed
             at ./home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/minstant-0.1.1/src/instant.rs:120:9
   9: risingwave_stream::executor::dispatch::DispatchExecutorInner::dispatch::{{closure}}
             at ./ebs/risingwave/src/stream/src/executor/dispatch.rs:85:29
  10: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
             at ./rustc/9067d5277d10f0f32a49ec9c125a33828e26a32b/library/core/src/future/mod.rs:91:19
  11: <async_stack_trace::StackTraced<F> as core::future::future::Future>::poll
             at ./ebs/risingwave/src/utils/async_stack_trace/src/lib.rs:171:23
  12: <futures_util::future::future::fuse::Fuse<Fut> as core::future::future::Future>::poll
             at ./home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-util-0.3.21/src/future/future/fuse.rs:86:37
  13: <risingwave_stream::executor::dispatch::DispatchExecutor as risingwave_stream::executor::StreamConsumer>::execute::{{closure}}
             at ./ebs/risingwave/src/stream/src/executor/dispatch.rs:272:22
  14: <futures_async_stream::try_stream::from_generator::GenTryStream<G> as futures_core::stream::Stream>::poll_next
             at ./home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-async-stream-0.2.5/src/lib.rs:430:31
  15: <core::pin::Pin<P> as futures_core::stream::Stream>::poll_next
             at ./home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-core-0.3.21/src/stream.rs:120:9
  16: <&mut S as futures_core::stream::Stream>::poll_next
             at ./home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-core-0.3.21/src/stream.rs:104:9
  17: <tokio_stream::stream_ext::next::Next<St> as core::future::future::Future>::poll
             at ./home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-stream-0.1.9/src/stream_ext/next.rs:42:9
  18: <tracing_futures::Instrumented<T> as core::future::future::Future>::poll
             at ./home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/tracing-futures-0.2.5/src/lib.rs:283:9
  19: <async_stack_trace::StackTraced<F> as core::future::future::Future>::poll
             at ./ebs/risingwave/src/utils/async_stack_trace/src/lib.rs:171:23
  20: <futures_util::future::future::fuse::Fuse<Fut> as core::future::future::Future>::poll
             at ./home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-util-0.3.21/src/future/future/fuse.rs:86:37
  21: risingwave_stream::executor::actor::Actor<C>::run::{{closure}}
             at ./ebs/risingwave/src/stream/src/executor/actor.rs:165:16

Downstream issue: https://github.com/singularity-data/risingwave/issues/4547