﻿Write a SpacetimeDB backend module in Rust that defines a sum type and uses it in multiple table columns.

TYPES
- Struct: Rect
  - Fields:
    - width: i32
    - height: i32
- Enum: Shape
  - Variants:
    - Circle(i32)
    - Rectangle(Rect)

TABLE
- drawing
  - Struct: Drawing
  - Fields:
    - id: i32 (primary key)
    - a: Shape
    - b: Shape

REDUCERS
- seed: insert exactly one row into drawing
  - (id=1, a=Shape::Circle(10), b=Shape::Rectangle(Rect { width:4, height:6 }))
