feat: add custom icon support with container styling for toast notifications

[sinner]

Define Icons by Toast Type: You can now provide custom icons for specific toast types directly through the toast options. This allows for more granular control over the appearance of your notifications. successIcon errorIcon loadingIcon Example: jsx toast.success('Successfully saved!', { successIcon: '🎉', });

toast.error('Something went wrong.', { errorIcon: '🔥', }); Custom Icon Container Style: A new iconContainerStyle option has been added to allow for custom styling of the icon's container using a CSS properties object. Example: jsx toast.success('Custom styled icon!', { iconContainerStyle: { border: '2px solid green', padding: '2px' } }); Changes Updated ToastOptions in src/types/toast.ts to include the new icon properties. Modified ToastBar.tsx to handle and render the new type-specific icons. Updated README.md to document the new features.