Make DayComponents initializer public for external use

[Rk1821389]

Details

This change updates the access control of the DayComponents initializer from internal to public. This enables developers to instantiate DayComponents directly when using the package via Swift Package Manager, which is currently impossible due to the restricted access level.

// Before
init(month: MonthComponents, day: Int) { ... }

// After
public init(month: MonthComponents, day: Int) { ... }