Function generate_proto_file 

pub fn generate_proto_file(
    schema: &CompiledSchema,
    package: &str,
    include_types: &[String],
    exclude_types: &[String],
) -> String

Generate a complete .proto file from a compiled schema.

Produces a proto3 service definition with:

• One message per GraphQL type (fields sorted alphabetically for stable numbering)
• One RPC per query (Get for single, List for list queries)
• One RPC per mutation (returns MutationResponse)
• Enum definitions from the schema
• Request/response wrapper messages

Errors

Returns an error if the schema contains no types to expose.