Write a SpacetimeDB backend module in Rust that defines a product table with a BTree-indexed price column, a result table, and a reducer that filters products within a price range and writes matches to the result table.

TABLES
- product
  - Struct: Product
  - Fields:
    - id: u64 (primary key, auto_inc)
    - name: String
    - price: u32 (index btree)

- price_range_result
  - Struct: PriceRangeResult
  - Fields:
    - product_id: u64 (primary key)
    - name: String
    - price: u32

REDUCERS
- find_in_price_range(ctx, min_price: u32, max_price: u32)
  - Iterate all products
  - For each product where price >= min_price AND price <= max_price, insert a PriceRangeResult row
