Retire the synthetic-pythonx assumptions from tests and docstrings #7

What

Four tests (test_runtime_module.py::TheModuleIsUnreachableByOrdinaryImport x2, test_ui_init_module.py::TheUiInitModuleIsUnreachableAndDead x2) assert that import pythonx.compose... does not load the files on disk, because the binder used to own sys.modules['pythonx'] with __path__ = []. The docstrings of runtime/__init__.py, ui/__init__.py, ui/modifier.py, ui/unit/__init__.py and layout/__init__.py describe the same structure.

Why

PythonMultiplatform d00f413f moved its layer to python_multiplatform.binding and pins that import pythonx loads the real package (KotlinNamedSurfaceTest.aRealPythonxPackageOnDiskIsWhatImportPythonxLoads). AGENTS.md §12 rules the synthetic structure out. SPEC Outside intent §1.

Done when

• The four tests assert the opposite: import pythonx.compose.runtime / .ui load this repository's files (__file__ under pythonx/), with the binder layer installed.
• No docstring describes a synthesised pythonx.
• Red observed before the change; suite counts recorded before and after.