pyproject(mypy): add sphinx_fonts to ignore_missing_imports

why: sphinx_fonts is a local docs/_ext extension, not an installed
package — mypy cannot resolve it at analysis time.
what:
- Add sphinx_fonts to [[tool.mypy.overrides]] ignore_missing_imports
- Add tests.docs._ext.test_sphinx_fonts to ignore_errors (mypy discovers
  sphinx_fonts as a top-level module in this repo, so arg-type errors
  from SimpleNamespace duck-typing need suppression)

Author: tony

pyproject.toml

@@ -135,6 +135,14 @@ files = [
   "tests/",
 ]
 
+[[tool.mypy.overrides]]
+module = ["sphinx_fonts"]
+ignore_missing_imports = true
+
+[[tool.mypy.overrides]]
+module = ["tests.docs._ext.test_sphinx_fonts"]
+ignore_errors = true
+
 [tool.ruff]
 target-version = "py310"