Add property to calculate and expose next run time of routine.

[adambirds]

Description

This PR adds a property next_run that calculates the next run time for the routine to the Routine class so that this can be exposed and used in other commands etc.

I have tested this on my own production twitch bot by installing from git and it works great.

Checklist

• [x] If code changes were made then they have been tested.
  • [ ] I have updated the documentation to reflect the changes. - couldn't find where to add the property. maybe auto generated from doc strings??
  • [ ] I have updated the changelog with a quick recap of my changes. - not sure which version number i would add it under.
• [ ] This PR fixes an issue.
• [x] This PR adds something new (e.g. new method or parameters).
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] This PR is not a code change (e.g. documentation, README, ...)
• [x] I have read and agree to the Developer Certificate of Origin for this contribution

[adambirds]

Is this able to be merged now? I have had this running for a few weeks now without an issue by installing direct from my branch but would be good to get merged.

[adambirds]

@chillymosh can this be merged?

[EvieePy]

@chillymosh can this be merged?

I will test it now

[EvieePy]

Ideally this would be a method, not a property. Logic after some testing works fine though