fix(enhanced-img): ensure ambient modules use ambient imports

Top-level imports and exports automatically upgrade a TypeScript file to
the module context. This is not desired in `ambient.d.ts` because we
want to keep this module ambient in order for the `declare module` to
apply globally across all imports of `*?enhanced`.

By importing the `Picture` type inside the ambient module context, we
preserve the "ambient-ness" of the `ambient.d.ts` file.

https://www.typescriptlang.org/docs/handbook/modules/reference.html#ambient-modules

Author: BastiDood

packages/enhanced-img/types/ambient.d.ts

@@ -1,6 +1,5 @@
-import type { Picture } from 'vite-imagetools';
-
 declare module '*?enhanced' {
+	import type { Picture } from 'vite-imagetools';
 	const value: Picture;
 	export default value;
 }