chore: add MyPy type checking config with baseline ignore rules

Adds [tool.mypy] section to pyproject.toml with permissive baseline settings
and disables error codes that fire against the existing untyped codebase.
Adds the mirrors-mypy pre-commit hook (v1.19.1) running over python/ at once.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.pre-commit-config.yaml

@@ -35,3 +35,12 @@ repos:
       - id: flake8
         files: ^python/
         args: [--config=.flake8]
+
+  - repo: https://github.com/pre-commit/mirrors-mypy
+    rev: "v1.19.1"
+    hooks:
+      - id: mypy
+        files: ^python/
+        args: [--config-file=pyproject.toml]
+        pass_filenames: false
+        additional_dependencies: []

pyproject.toml

@@ -10,3 +10,27 @@ target-version = ["py310"]
 [tool.isort]
 profile = "black"
 line_length = 100
+
+[tool.mypy]
+python_version = "3.10"
+warn_return_any = false
+warn_unused_configs = true
+ignore_missing_imports = true
+check_untyped_defs = false
+disallow_untyped_defs = false
+disable_error_code = [
+    "arg-type",
+    "attr-defined",
+    "union-attr",
+    "call-arg",
+    "assignment",
+    "var-annotated",
+    "annotation-unchecked",
+    "index",
+    "has-type",
+    "dict-item",
+    "misc",
+    "list-item",
+    "return-value",
+    "operator",
+]