Keep package namespace clean under lazy init

Alias the internal 'importlib'/'typing' imports to '_importlib'/'_typing' so
they no longer leak as public attributes of 'python_utils' (they appeared in
dir() and as python_utils.importlib / python_utils.typing under the lazy
__init__, which develop did not expose). Add an explicit '# pragma: no cover'
to the TYPE_CHECKING block since coverage's auto-exclusion only matches the
unaliased 'typing.TYPE_CHECKING' spelling.

Verified via a full public-API manifest diff against develop: the only
remaining differences are the two inherent consequences of deferring asyncio
(aio_timeout_generator's default iterable is now None instead of aio.acount,
and python_utils.time no longer re-exposes the 'aio'/'asyncio' modules).

Author: wolph

python_utils/__init__.py

@@ -55,10 +55,10 @@
     LoggerBase
 """
 
-import importlib
-import typing
+import importlib as _importlib
+import typing as _typing
 
-if typing.TYPE_CHECKING:
+if _typing.TYPE_CHECKING:  # pragma: no cover
     # Eager imports for type checkers only; the runtime equivalents are loaded
     # lazily by ``__getattr__`` below. Names appear in ``__all__`` so they are
     # treated as re-exports (not unused imports).
@@ -155,12 +155,14 @@
 }
 
 
-def __getattr__(name: str) -> typing.Any:
+def __getattr__(name: str) -> _typing.Any:
     """Lazily import submodules and their exported names on first access."""
     if name in _SUBMODULES:
-        module = importlib.import_module(f'.{name}', __name__)
+        module = _importlib.import_module(f'.{name}', __name__)
     elif name in _NAME_TO_MODULE:
-        module = importlib.import_module(f'.{_NAME_TO_MODULE[name]}', __name__)
+        module = _importlib.import_module(
+            f'.{_NAME_TO_MODULE[name]}', __name__
+        )
         value = getattr(module, name)
         globals()[name] = value  # cache so __getattr__ runs only once
         return value