👨‍💻 Add types declaration file

[climba03003]

Closes #17

It should be good for the initial types.
I do not change the package.json since this package provide both cjs and esm.
Having the types field may get things weird in types resolving.
.d.cts should match .cjs and .d.ts should match .js automatically.

[climba03003]

I see some improvement can be done.
For example the cronjob function, task structure that added to database, etc

[dr-dimitru]

it can be strings like in case of Redis, or what do you mean exactly?

[climba03003]

For what I means is that the Function can be more specific in TypeScript.

The task: object can also be standardize to a proper struct.

[dr-dimitru]

@climba03003 function<any|Promise<any>>?

[climba03003]

It would be something like

(
  ready: (
    (next: Date) => void) | 
    ((callback: (err: Error, success: boolean) => void) => void)
  )
) => Promise<void> | void

[dr-dimitru]

@climba03003

1. Callback is gone
2. Should include only ready

[dr-dimitru]

@climba03003 lmk if it's good to go or we still want to change something

[climba03003]

lmk if it's good to go or we still want to change something

Sorry for that late reply. A bit busy.

The current one is good to go.