OTP Input component

**Is your feature request related to a problem? Please describe.**
OTP / verification code input is a common requirement, but react-native-paper does not provide a dedicated component. Developers must build custom solutions or rely on third-party libraries.

**Describe the solution you'd like**
Add a built-in OTP Input component that works with the existing react-native-paper theme and components.

**Describe alternatives you've considered**
Using third-party libraries.

**Additional context**
This is a common pattern in authentication flows (login, signup, 2FA) and would improve consistency and developer experience.

The issue names no files, tests, or entry points. Start by reviewing existing react-native-paper components and theme integration to determine the scope and API for an OTP Input component. Done would require an agreed design plus a built-in component that works consistently with the existing theme and components.

Written by the indexing model from the issue text.