Fix Git.version_info pickling

For #1836.

This uses a property with the same logic as before for version_info
caching, except that the _version_info backing attribute holds the
value None, rather than being unset, for the uncomputed state. This
rectifies the inconistency between the property's behavior and the
way the associated states are represented by its __setstate__ and
__getstate__ methods for pickling.

Because the Git class only used LazyMixin as an implementation
detail of the version_info attribute, it is removed as a subclass.

git/cmd.py

@@ -25,7 +25,6 @@
     UnsafeProtocolError,
 )
 from git.util import (
-    LazyMixin,
     cygpath,
     expand_path,
     is_cygwin_git,
@@ -287,7 +286,7 @@ def dict_to_slots_and__excluded_are_none(self: object, d: Mapping[str, Any], exc
 ## -- End Utilities -- @}
 
 
-class Git(LazyMixin):
+class Git:
     """The Git class manages communication with the Git binary.
 
     It provides a convenient interface to calling the Git binary, such as in::
@@ -784,6 +783,7 @@ def __init__(self, working_dir: Union[None, PathLike] = None):
         self._environment: Dict[str, str] = {}
 
         # Cached command slots
+        self._version_info: Union[Tuple[int, int, int, int], None] = None
         self.cat_file_header: Union[None, TBD] = None
         self.cat_file_all: Union[None, TBD] = None
 
@@ -795,8 +795,8 @@ def __getattr__(self, name: str) -> Any:
             Callable object that will execute call :meth:`_call_process` with
             your arguments.
         """
-        if name[0] == "_":
-            return LazyMixin.__getattr__(self, name)
+        if name.startswith("_"):
+            return super().__getattribute__(name)
         return lambda *args, **kwargs: self._call_process(name, *args, **kwargs)
 
     def set_persistent_git_options(self, **kwargs: Any) -> None:
@@ -811,20 +811,6 @@ def set_persistent_git_options(self, **kwargs: Any) -> None:
 
         self._persistent_git_options = self.transform_kwargs(split_single_char_options=True, **kwargs)
 
-    def _set_cache_(self, attr: str) -> None:
-        if attr == "_version_info":
-            # We only use the first 4 numbers, as everything else could be strings in fact (on Windows).
-            process_version = self._call_process("version")  # Should be as default *args and **kwargs used.
-            version_numbers = process_version.split(" ")[2]
-
-            self._version_info = cast(
-                Tuple[int, int, int, int],
-                tuple(int(n) for n in version_numbers.split(".")[:4] if n.isdigit()),
-            )
-        else:
-            super()._set_cache_(attr)
-        # END handle version info
-
     @property
     def working_dir(self) -> Union[None, PathLike]:
         """:return: Git directory we are working on"""
@@ -838,6 +824,16 @@ def version_info(self) -> Tuple[int, int, int, int]:
 
             This value is generated on demand and is cached.
         """
+        if self._version_info is None:
+            # We only use the first 4 numbers, as everything else could be strings in fact (on Windows).
+            process_version = self._call_process("version")  # Should be as default *args and **kwargs used.
+            version_numbers = process_version.split(" ")[2]
+
+            self._version_info = cast(
+                Tuple[int, int, int, int],
+                tuple(int(n) for n in version_numbers.split(".")[:4] if n.isdigit()),
+            )
+
         return self._version_info
 
     @overload