fix: prevent discriminated models from being created before their base model

[karrui]

Problem

Using EncryptSubmission Model without having compiled Submission Model causes EncryptSubmission Model to be without core keys like form

This problem extends to Form model as well.

Closes #243

Solution

Bug Fixes:

• Fix possible race conditions by only returning discriminated models after compiling/retrieving their base instead of compiling from scratch.

Note: The usual way of exporting discriminated models should be employed once we have fully migrated over to Typescript.

export const EmailFormModel = FormModel.discriminator(ResponseMode.Email, EmailFormSchema)
export const EncryptFormModel = FormModel.discriminator(ResponseMode.Encrypt, EncryptedFormSchema)