Write a SpacetimeDB backend module in Rust that defines one table and two reducers: one that inserts a row and one that updates a row.

TABLE
- user
  - Struct: User
  - Fields:
    - id: u64 (primary key, auto_inc)
    - name: String
    - age: i32
    - active: bool

REDUCERS
- insert_user: given name:String, age:i32, active:bool, insert a new row (id is auto-assigned)
- update_user: given id:u64, name:String, age:i32, active:bool, update the row in user with id=id to exactly these values
  - (id=id, name=name, age=age, active=active)
