docs: add git lib to mdbook toolset

docs/preprocessors/libs/__init__.py

@@ -0,0 +1 @@
+__all__ = ["git"]

docs/preprocessors/libs/git.py

@@ -0,0 +1,41 @@
+from collections import namedtuple
+import os
+from pathlib import Path, PurePath
+import shlex
+import subprocess
+
+
+class Git:
+    """Use git commands in mdbook preprocessors"""
+
+    def __init__(self, cwd: PurePath | str) -> None:
+        self._cwd = Path(cwd)
+        self._environ = os.environ.copy()
+        self._environ["LC_ALL"] = "C"
+
+    class CommandOutput(namedtuple("CommandOutput", ["stdout", "stderr"])):
+        def __str__(self) -> str:
+            return self.stdout
+
+    def _git(self, commands: list[str] | str) -> CommandOutput:
+        """Run a git command
+
+        Args:
+            commands (list[str] | str): commands and args passed to git.
+
+        Returns:
+            CommandOutput: Tuple containing `stdout` and `stderr`
+        """
+        if type(commands) is str:
+            commands = shlex.split(commands)
+        proc = subprocess.run(
+            ["git", *commands],
+            capture_output=True,
+            text=True,
+            env=self._environ,
+            cwd=self._cwd,
+        )
+        return self.CommandOutput(stdout=proc.stdout, stderr=proc.stderr)
+
+    def log(self, *args: str) -> CommandOutput:
+        return self._git(["log", *args])