Write a SpacetimeDB backend module in C# 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: ulong (primary key, AutoInc)
    - Name: string
    - Price: uint (index BTree)

- PriceRangeResult
  - Struct: PriceRangeResult
  - Fields:
    - ProductId: ulong (primary key)
    - Name: string
    - Price: uint

REDUCERS
- FindInPriceRange(ctx, uint minPrice, uint maxPrice)
  - Iterate all products
  - For each product where Price >= minPrice AND Price <= maxPrice, insert a PriceRangeResult row
