`ignisDate` should allow string and number arguments

The underlying `format` function from `date-fns` actually accepts and parses following:

```ts
export type DateArg = DateType | number | string;
```

It doesn't make sense to narrow this down to `Date` only as `ignisDate` currently does.

Search the TypeScript source for `ignisDate` and inspect how it passes arguments to the `date-fns` `format` function. Done means the public typing accepts Date, string, and number arguments while preserving the existing Date case.

Written by the indexing model from the issue text.