fix nextRun with singleton mode reporting incorrect time

[JohnRoesler]

What does this do?

adjusts how the nextScheduledRun field is tracked. Rather than being a single time.Time field it is now a slice of time.Time. This allows for the case, that will often happen with limited/singleton jobs that may be queued up. In this case, there are multiple nextScheduledRun values.

Which issue(s) does this PR fix/relate to?

resolves #704

List any changes that modify/break current functionality

Have you included tests for your changes?

yes - thank you @aneesh1 for the excellent ticket write up and test case

Did you document any new/modified functionality?

• Updated example_test.go
• Updated README.md

Notes

[aneesh1]

(If you already have a test for this, feel free to ignore) Do we have / can we add a test where a job runs longer than the specified duration and the next job has to wait to highlight the expected behavior?

Ex:

• Add DurationJob(5 * time.Second)
• t0: startJob (expecting job to run again at t5)
• t5: job is still running, so it’s skipped
• t7: job finishes
• t10: next job starts

cc @drewgonzales360

[drewgonzales360]

Thanks for all the hard work on this 🙏

[JohnRoesler]

When you all could, please validate it's working as expected for you: v2.2.10-rc1