Generating Custom Field

This handles Salesforce custom field metadata generation with a strong focus on the stuff that actually breaks during deployment. It knows the difference between Master-Detail and Lookup relationships, enforces precision and scale rules for numbers, and won't let you add forbidden attributes like `required` or `deleteConstraint` to Master-Detail fields. The spec is opinionated about inline help text and descriptions being mandatory, which will annoy you until you've debugged your third cryptic deployment error. Honestly most useful for roll-up summaries and relationship fields where the metadata constraints are finicky. If you're just making text fields you probably don't need this level of hand-holding, but it'll save you round trips to the Metadata API when working with the complicated types.