fix(types): improve type-safety for cron callback functions

[renejfc]

About

This PR introduces better type safety for callback functions in the Cron implementation:

Summary

• Adds a proper CronCallback type definition to explicitly type the callback function parameters and return value
• Replaces generic Function type with the more specific CronCallback type
• Introduces isCronCallback type guard to safely check callback types at runtime
• Updates test to leverage improved typing
• Maintains backward compatibility while providing better type inference

Checks

• all tests passing
• pre-commit task passing
• docs for new definitions added

---

These changes help catch potential type-related issues at compile time and provide better IDE support.

Note: This is a type-safety improvement with no runtime behavior changes.

[renejfc]

My mistake—I worked directly from the master branch. Thanks for taking care of it!

Also, please feel free to change/adjust as you see fit.

[Hexagon]

LGTM

[Hexagon]

Thanks 👍

[Hexagon]

Released to npm dev channel through 9.0.1-dev.2