Write a SpacetimeDB backend module in Rust that defines a table with a unique constraint on a non-primary-key column and a reducer that inserts rows.

TABLES
- account
  - Struct: Account
  - Fields:
    - id: u64 (primary key, auto_inc)
    - email: String (unique)
    - display_name: String

REDUCERS
- create_account(ctx, email: String, display_name: String)
  - Insert an Account row with the given email and display_name
  - Use id: 0 for auto_inc
