Add warning when string is passed to transition prop

[sagarpaul9475]

What this does

Adds a developer warning when a string (e.g., "Bounce") is passed to the transition prop of ToastContainer.

Why

The transition prop expects a transition component (like transition={Bounce}), but beginners may accidentally pass a string like "Bounce", which fails silently. This warning will improve developer experience.

Example

// ❌ This will trigger a warning
<ToastContainer transition="Bounce" />

// ✅ This is correct
import { Bounce } from 'react-toastify';
<ToastContainer transition={Bounce} />

[Link2Twenty]

Typescript will already catch this for you.

You'll get the error

Type 'string' is not assignable to type 'ToastTransition | undefined'.