Write a SpacetimeDB backend module in C# that defines one table and a reducer that performs insert, update, and delete in one call.

TABLE
- User
  - Struct: User
  - Fields:
    - Id: int (primary key)
    - Name: string
    - Age: int
    - Active: bool

REDUCERS
- Crud: perform these steps in order
  - insert (Id=1, Name="Alice", Age=30, Active=true)
  - insert (Id=2, Name="Bob",   Age=22, Active=false)
  - update (Id=1, Name="Alice2", Age=31, Active=false)
  - delete Id=2
