Function generate_module 

pub fn generate_module(
    fds: &FileDescriptorSet,
    options: &CodegenOptions,
) -> Result<ModuleTree, CodegenError>

Generate a structured module tree from a FileDescriptorSet.

Unlike generate_with_options which returns a flat String, this returns a ModuleTree that preserves the package hierarchy, enabling per-package or per-file output.

Errors

Returns a CodegenError if the descriptor set is invalid.