Enable mypy pre-commit hook

Change-Id: I266a2866627fcf66d0f5111c9237a37e55414685

.pre-commit-config.yaml

@@ -47,6 +47,16 @@ repos:
       - id: hacking
         additional_dependencies: ['neutron', 'neutron-lib']
         exclude: '^(doc|releasenotes|tools)/.*$'
+  - repo: https://github.com/pre-commit/mirrors-mypy
+    rev: v1.14.1
+    hooks:
+      - id: mypy
+        args: [--config-file=./mypy.ini]
+        pass_filenames: false
+        # need to list alembic here; otherwise it doesn't see internals
+        # necessary to detect one of 'ignored' errors and complains about
+        # unnecessary ignore; other dependencies can be left out it seems
+        additional_dependencies: ['alembic']
   - repo: local
     hooks:
       - id: flake8

mypy.ini

@@ -12,6 +12,8 @@ disable_error_code = import-untyped,var-annotated,import-not-found
 # honor excludes by not following there through imports
 follow_imports = silent
 
+files = neutron
+
 # NOTE: Gradually enable type checking for each package.
 # Finally, when the whole repo is migrated this option can be deleted
 # and rules applied to the whole repo.

tox.ini

@@ -123,7 +123,7 @@ commands =
 
 [testenv:mypy]
 deps = {[testenv:pep8]deps}
-commands = mypy --config-file ./mypy.ini neutron
+commands = mypy --config-file ./mypy.ini
 
 [testenv:releasenotes]
 description =