add RTT in output once it is able to detect the open port

**Is your feature request related to a problem? Please describe.**
no, not related to any issue.

**Describe the solution you'd like**
I have a use case, that I have a list of servers, I need to monitor RTT(round trip time) or timeout in case service is dead. Eventually, I will save this output into influxDB, and graph it on Grafana.

**Describe alternatives you've considered**
I have not been able to find out any alternative solution existed.

**Additional context**
Thanks much for looking into the PR, I am unsure if it makes sense to add it in this app at all.

The issue names no files, tests, or entry points. First establish whether RustScan should expose RTT and timeout data, then define the output format and how it could feed InfluxDB and Grafana; done means the scope and acceptance criteria are agreed before implementation.

Written by the indexing model from the issue text.