Refactor: use monadic operators and prefer NonZeroU64 for seconds

[BastiDood]

Hello there! Fun little project here. Figured that a little bit of cleanup would be appreciated. In this PR:

• I transformed the long, nested match statements into their monadic counterparts so that the control flow is more "flat" and "linear", so to speak.
• I replaced the seconds option to take in an Option<NonZeroU64> instead of an Option<u64>. This allows the compiler to optimize for memory layout. The former ensures that seconds is represented in memory as if it were a plain u64 (which is not the case for the latter). Moreover, it doesn't make sense to provide zero delay, anyway. 😅
• Finally, I ensured that the program panics if it can't move the mouse. I figured that this would be the intentional behavior so that there are no surprises in case errors do arise.

That is all. Thanks! 🎉