Large commit to make Pint more typing friendly

In this very large commit we tackle a few aspects of Pint that
makes it difficult to do static typing.

1. Dynamic classes became static: Quantity and Unit are now
(for the most part) static classes with a static inheritance.
This allows mypy/pylance and other type checker to properly
inspect them.

2. Added types through out all the code. (WIP)

3. Refactor minor parts of the code to make it more typing
homogeneous. Catch a few potential bugs in the way.

4. Add several TODOs that need to be addressed in 0.23

5. Moved some group and system and context code out of the PlainRegistry

6. Moved certain specialized methods out of the PlainRegistry.

1 files changed, 12 insertions, 2 deletions

diff --git a/pint/compat.py b/pint/compat.py
index 7b48efa..727ff99 100644
--- a/pint/compat.py
+++ b/pint/compat.py
@@ -20,6 +20,16 @@ from collections.abc import Mapping
 from typing import Any, NoReturn, Callable
 from collections.abc import Generator, Iterable
 
+try:
+    from typing import TypeAlias  # noqa
+except ImportError:
+    from typing_extensions import TypeAlias  # noqa
+
+try:
+    from typing import Self  # noqa
+except ImportError:
+    from typing_extensions import Self  # noqa
+
 
 def missing_dependency(
     package: str, display_name: str | None = None
@@ -137,10 +147,10 @@ except ImportError:
     HAS_UNCERTAINTIES = False
 
 try:
-    from babel import Locale as Loc
+    from babel import Locale
     from babel import units as babel_units
 
-    babel_parse = Loc.parse
+    babel_parse = Locale.parse
 
     HAS_BABEL = hasattr(babel_units, "format_unit")
 except ImportError: