Add secondary key indexing without indexed keys being unique#16

For more context, view discussions at #4 Basically, currently, if we have ```typescript const User = z.object({ email: z.string().describe('index') }) ``` It will use keys such as `user_by_email` / `(email)` -> `User` Which is fine for unique keys like `email`, but if we want something like the following, it doesnt work; ```typescript const User = z.object({ favoriteColor: z.string().describe('index') }) ``` Because then we will have It will use keys such as `user_by_favoriteColor` / `(favorite color)` -> `User` Which will be overwritten every time a new user is created. To solve this, we need to just add one more key part if the index is not unique, like the following: [From Deno's Docs](https://deno.com/[email protected]/runtime/kv/secondary_indexes) ```typescript const byColorKey = ["users_by_favorite_color", user.favoriteColor, user.id]; ```