fix: Let dataclass implement __init__ method, set extra fields in get_options

With our own `__init__` implementation, unpassed fields would never be set on the instance, triggering attribute errors.

Let dataclass do its job, add set extra fields from outside of the class.

Author: pawamoy

src/mkdocstrings_handlers/python/config.py

@@ -843,15 +843,6 @@ def _extract_extra(cls, data: dict[str, Any]) -> tuple[dict[str, Any], dict[str,
         copy = data.copy()
         return {name: copy.pop(name) for name in data if name not in field_names}, copy
 
-    # YORE: Bump 2: Remove block.
-    def __init__(self, **kwargs: Any) -> None:
-        """Initialize the instance."""
-        extra_fields = self._extract_extra(kwargs)
-        for name, value in kwargs.items():
-            object.__setattr__(self, name, value)
-        if extra_fields:
-            object.__setattr__(self, "_extra", extra_fields)
-
     @classmethod
     def coerce(cls, **data: Any) -> MutableMapping[str, Any]:
         """Coerce data."""

src/mkdocstrings_handlers/python/handler.py

@@ -186,12 +186,17 @@ def get_options(self, local_options: Mapping[str, Any]) -> HandlerOptions:
 
         extra = {**self.global_options.get("extra", {}), **local_options.get("extra", {})}
         options = {**self.global_options, **local_options, "extra": extra}
-        # YORE: Bump 2: Replace `, **unknown_extra` with `` within line.
         try:
-            return PythonOptions.from_data(**options, **unknown_extra)
+            # YORE: Bump 2: Replace `opts =` with `return` within line.
+            opts = PythonOptions.from_data(**options)
         except Exception as error:
             raise PluginError(f"Invalid options: {error}") from error
 
+        # YORE: Bump 2: Remove block.
+        for key, value in unknown_extra.items():
+            object.__setattr__(opts, key, value)
+        return opts
+
     def collect(self, identifier: str, options: PythonOptions) -> CollectorItem:  # noqa: D102
         module_name = identifier.split(".", 1)[0]
         unknown_module = module_name not in self._modules_collection