refactor: extract the parametrization core into _pytest.parametrize

Move IdMaker, CallSpec and _ascii_escaped_by_config out of python.py
into a new module, together with the long-str id strategy literals they
own. python.py imports them back, so _pytest.python.CallSpec and the
CallSpec2 alias keep resolving as before.

Pure move, no behaviour change. The two CollectError call sites go
through a small _collect_error() helper which imports nodes lazily, so
nodes stays free to import this module later.

Author: RonnyPfannschmidt

changelog/14856.misc.rst

@@ -0,0 +1,4 @@
+Moved the parametrization core out of ``_pytest.python`` into the new
+``_pytest.parametrize`` module: ``CallSpec``, ``IdMaker`` and the id strategy
+literals. ``_pytest.python`` re-exports them, so ``_pytest.python.CallSpec`` and
+the deprecated ``CallSpec2`` alias keep working.

src/_pytest/fixtures.py

@@ -84,7 +84,7 @@
 
 
 if TYPE_CHECKING:
-    from _pytest.python import CallSpec
+    from _pytest.parametrize import CallSpec
     from _pytest.python import Function
     from _pytest.python import Metafunc
     from _pytest.reports import CollectReport