Currently, artillery-core detect time out responses by comparing two times based on SystemTime, see [code](https://github.com/bastion-rs/artillery/blob/badac7d5519cfd6ef5078262cad7769a4d361bce/artillery-core/src/epidemic/state.rs#L262-L270) But using SystemTime to detect time out could lead to weird behavior as it is not monotonic. Would be nice to use `Instant` instead.
