﻿Write a SpacetimeDB backend module in Rust that defines a table, a non-reducer helper function, and a reducer that uses the helper.

TABLE
- result
  - Struct: ResultRow
  - Fields:
    - id: i32 (primary key)
    - sum: i32

HELPERS
- add: given a:i32 and b:i32, returns i32

REDUCERS
- compute_sum: given id:i32, a:i32, b:i32, insert exactly this row into result
  - (id=id, sum=add(a, b))
