fix: Create proper nested module structure for wit_bindgen::rt

The generated code expects crate::wit_bindgen::rt::run_ctors_once() but
the previous implementation only did `pub use wit_bindgen_rt as wit_bindgen;`
which made wit_bindgen an alias, not a module with an rt submodule.

Fixed by creating the proper nested structure:
  pub mod wit_bindgen {
      pub use wit_bindgen_rt as rt;
  }

This provides:
  - crate::wit_bindgen (module)
  - crate::wit_bindgen::rt (wit_bindgen_rt crate)

Fixes error:
  error[E0433]: failed to resolve: could not find `rt` in `wit_bindgen`
  --> hello_component_wrapper_guest.rs:113:29
  |
  113 |         crate::wit_bindgen::rt::run_ctors_once();
  |                             ^^ could not find `rt` in `wit_bindgen`

Author: claude

rust/rust_wasm_component_bindgen.bzl

@@ -55,13 +55,14 @@ def _generate_wrapper_impl(ctx):
     """Generate a wrapper that includes both bindings and runtime shim"""
     out_file = ctx.actions.declare_file(ctx.label.name + ".rs")
 
-    # Create wrapper content - re-export wit-bindgen-rt as wit_bindgen
+    # Create wrapper content - create nested module structure for wit-bindgen-rt
     # The wit-bindgen CLI generates code that expects: crate::wit_bindgen::rt
     # The CLI also generates the export! macro with --pub-export-macro flag
     wrapper_content = """// Generated wrapper for WIT bindings
 //
-// This wrapper re-exports wit-bindgen-rt as wit_bindgen to provide the runtime
-// at the path expected by wit-bindgen CLI (--runtime-path crate::wit_bindgen::rt)
+// This wrapper creates a wit_bindgen module with rt submodule that re-exports
+// wit-bindgen-rt crate. This provides the runtime at the path expected by
+// wit-bindgen CLI (--runtime-path crate::wit_bindgen::rt)
 //
 // The export! macro is generated by wit-bindgen CLI (via --pub-export-macro)
 
@@ -70,9 +71,11 @@ def _generate_wrapper_impl(ctx):
 #![allow(unused_imports)]
 #![allow(dead_code)]
 
-// Re-export wit-bindgen-rt as wit_bindgen to provide the runtime module
-// This provides wit_bindgen::rt with proper allocator integration
-pub use wit_bindgen_rt as wit_bindgen;
+// Create nested module structure: wit_bindgen::rt
+// The wit-bindgen CLI expects crate::wit_bindgen::rt::run_ctors_once() etc.
+pub mod wit_bindgen {
+    pub use wit_bindgen_rt as rt;
+}
 
 // Generated bindings follow (including export! macro):
 """