[BUG] - Handling negative time.Duration as interval param to Every func

[husam-e]

Describe the bug

Not sure if this is a bug, more of a question to confirm expected behavior: currently no error is returned when a negative time.Duration is provided as the interval param to Every. Is that intentional? Should it not return an error and fail fast, similar to when providing a negative int? Not clear to me what the intended behavior is for that.

To Reproduce

Steps to reproduce the behavior:

scheduler := gocron.NewScheduler(time.UTC)
interval := -1 * time.Second
_, err := scheduler.Every(interval).Do(func() { })

Version

v1.35.2

Expected behavior

err is returned non-nil, or otherwise behavior for negative Duration is documented on the Every function.

Additional context

Thinking it would be helpful as input validation to get an error in this scenario to immediately recognize invalid setup, just like how negative int values are treated as errors.

[JohnRoesler]

@husam-e I agree this is a bug. it's solved in v2. If you'd like to open a PR for v1 feel free 😄