Add mypy to pre-commit and fix the errors

Limit the Python version to =3.10 because of the
`pandas-stubs` typing dependency, see:
pandas-dev/pandas-stubs#400
Poetry command:
```sh
poetry add -G typing mypy pandas-stubs
```
Add the recommended settings for mypy:
https://blog.wolt.com/engineering/2021/09/30/professional-grade-mypy-configuration/
Fix the errors with type ignore as they originate from
wrong typing in pandas/builtin libs and make sure
mypy passes:
```sh
pre-commit run mypy --all-files
```

.pre-commit-config.yaml

@@ -25,3 +25,8 @@ repos:
         entry: poetry run pylint
         language: system
         types: [python]
+      - id: mypy
+        name: mypy
+        entry: poetry run mypy
+        language: system
+        types: [python]

pyproject.toml

@@ -26,14 +26,18 @@ classifiers = [
 ]
 
 [tool.poetry.dependencies]
-python = "^3.10"
+python = ">= 3.10, < 3.11"
 pandas = "^1.5.1"
 beautifulsoup4 = {version = "^4.11.1", extras = ["lxml", "html5lib"]}
 
 [tool.poetry.group.dev.dependencies]
 pre-commit = "^2.20.0"
 pylint = "^2.15.6"
 
+[tool.poetry.group.typing.dependencies]
+mypy = "^0.991"
+pandas-stubs = "^1.5.1.221024"
+
 [tool.poetry.urls]
 "Bug Tracker" = "https://github.com/jond01/xil/issues"
 
@@ -43,6 +47,13 @@ profile = "black"
 [tool.pylint]
 enable = ["I"]
 
+[tool.mypy]
+check_untyped_defs = true
+disallow_untyped_defs = true
+warn_unused_ignores = true
+warn_return_any = true
+show_error_codes = true
+
 [build-system]
 requires = ["poetry-core"]
 build-backend = "poetry.core.masonry.api"

xil/_headers.py

@@ -24,4 +24,4 @@ def get_url_response(
         else:
             headers = {}
     request = urllib.request.Request(url, headers=headers)
-    return urllib.request.urlopen(request)
+    return urllib.request.urlopen(request)  # type: ignore[no-any-return]

xil/fibi.py

@@ -26,7 +26,11 @@
 
 with get_url_response(_FIBI_URL) as response:
     dfs = pd.read_html(
-        response, match=_MATCH, header=_HEADER, encoding=_ENCODING, attrs=_ATTRS
+        response,  # type: ignore[arg-type]
+        match=_MATCH,
+        header=_HEADER,
+        encoding=_ENCODING,
+        attrs=_ATTRS,
     )
 
 df = dfs[0]  # It is guaranteed to have at least one element - otherwise an exception

xil/union.py

@@ -24,7 +24,7 @@
 _HEADER = [0, 1]
 
 with get_url_response(_UNION_URL, headers=_UNION_HEADERS) as response:
-    df = pd.read_html(response, header=_HEADER)[0]
+    df = pd.read_html(response, header=_HEADER)[0]  # type: ignore[arg-type]
 
 df = df.drop(("Unnamed: 7_level_0", "מכירה"), axis=1)  # empty (NaNs) column