Fix deps when used as a library

[alexgleason]

When trying to use this library from deno.land, my application crashes on start with this error:

Watcher File change detected! Restarting!
error: Relative import path "zod" not prefixed with / or ./ or ../ and not in import map from "https://deno.land/x/dongoose@1.0.1/src/schema.ts"
    at https://deno.land/x/dongoose@1.0.1/src/schema.ts:2:19
Watcher Process finished. Restarting on file change...

This MR fixes it by creating a deps.ts and deps_test.ts. Deno can't use import maps for libraries since it doesn't know the URL of the import map. So when the project is a library it has to be this way.

[roonie007]

LGTM