Create Custom Zod Schemas and Validate project-specific data

In this less we create a custom Zod schema using z.custom.

The example case covers room numbers validation: it must start with an uppercase letter followed by three digits. z.custom allows the creation of a brand new custom schema with a callback function that returns a boolean indicating validity.

We highlight a challenge with type inference in Zod's custom schemas: callback parameter types don't get aligned automatically - type-safety must be explicitly defined using type parameters.

We run tests against various room numbers and demonstrate how to effectively validate inputs and manage error messages.