feat(image): export ImageInst type

close tusen-ai#6479

src/image/index.ts

@@ -1,5 +1,5 @@
 export { default as NImage, imageProps } from './src/Image'
-export type { ImageProps } from './src/Image'
+export type { ImageProps, ImageInst } from './src/Image'
 export { default as NImageGroup, imageGroupProps } from './src/ImageGroup'
 export type { ImageGroupProps } from './src/ImageGroup'
 export type * from './src/public-types'