Lint Python type signatures using mypy

.local/bin/dirtree-changed

@@ -8,7 +8,7 @@ def get_subtree_mtime(root: str | Path) -> float:
     from os import walk
     from os.path import getmtime
 
-    maxtime = 0
+    maxtime = 0.0
 
     for dirname, _, filenames in walk(root):
         dirpath = Path(dirname)

.pre-commit-config.yaml

@@ -17,6 +17,10 @@ repos:
   rev: 5.12.0
   hooks:
   - id: isort
+- repo: https://github.com/pre-commit/mirrors-mypy
+  rev: v1.7.1
+  hooks:
+  - id: mypy
 - repo: https://github.com/syntaqx/git-hooks
   rev: v0.0.18
   hooks: