Function setDay

setDay(date: Date, day: number): Date
Sets the day of the month and returns a new Date instance.
Parameters
- date: Date
  The original date.
- day: number
  The day of the month to set.
Returns Date
A new Date with the updated day.
Example
```
setDay(new Date('2025-01-01'), 15); // → 2025-01-15
```
- Defined in date/set.ts:43