use TypedDict for return type of legacy detect() (#469)

---------

Co-authored-by: TAHRI Ahmed R. <[email protected]>

charset_normalizer/legacy.py

@@ -1,13 +1,24 @@
-from typing import Any, Dict, Optional, Union
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Any, Optional
 from warnings import warn
 
 from .api import from_bytes
 from .constant import CHARDET_CORRESPONDENCE
 
+# TODO: remove this check when dropping Python 3.7 support
+if TYPE_CHECKING:
+    from typing_extensions import TypedDict
+
+    class ResultDict(TypedDict):
+        encoding: Optional[str]
+        language: str
+        confidence: Optional[float]
+
 
 def detect(
     byte_str: bytes, should_rename_legacy: bool = False, **kwargs: Any
-) -> Dict[str, Optional[Union[str, float]]]:
+) -> ResultDict:
     """
     chardet legacy method
     Detect the encoding of the given byte string. It should be mostly backward-compatible.