codecs: add missing function, reflect runtime import * (#7918)

test_cases/stdlib/test_codecs.py

@@ -0,0 +1,13 @@
+# pyright: reportUnnecessaryTypeIgnoreComment=true
+
+import codecs
+from typing_extensions import assert_type
+
+assert_type(codecs.decode("x", "unicode-escape"), str)
+assert_type(codecs.decode(b"x", "unicode-escape"), str)
+
+assert_type(codecs.decode(b"x", "utf-8"), str)
+codecs.decode("x", "utf-8")  # type: ignore[call-overload]
+
+assert_type(codecs.decode("ab", "hex"), bytes)
+assert_type(codecs.decode(b"ab", "hex"), bytes)