Why

• Type checkers were raising errors
• Library could only be used when it was installed with the all extra. Otherwise, it threw import errors.

What was done

• Updated the return types of the Model functions e.g. HashModel, MongoModel etc.
• Fixed import errors when only one of the following extras is installed: sql, redis, mongo
• Updated Github actions to test for each scenario where the test extra is installed with any one of the extras sql, redis, mongo.