Satisfy MyPy's 'strict' type checks

This amends those parts of code that wouldn't pass MyPy's "strict" type checking.

Author: amn

src/csspring/syntax/parsing.py

@@ -510,7 +510,7 @@ def normalize_input(input: NormalizeInput) -> Input:
     if isinstance(input, Input):
         return input
     try:
-        input = iter(cast(Iterable, input))
+        input = iter(cast(Iterable[Any], input))
     except TypeError:
         assert not isinstance(input, Iterable) # Communicate to the type checker that `input` is not iterable
     else:
@@ -547,7 +547,7 @@ def source(element: Product | Token) -> str:
     """
     return element.source if hasattr(element, 'source') else ''.join(source(item) for item in element)
 
-def tokens(product: Iterable | Token) -> Iterator[Token]:
+def tokens(product: Product | Token) -> Iterator[Token]:
     """
     Yield every token contained in a parser production.
 

src/csspring/values.py

@@ -111,7 +111,7 @@ class TokenProduction(Production):
     """Class of productions that express a token, optionally one with a matching set of attributes.
     """
     type: type[Token]
-    attributes: Mapping
+    attributes: Mapping[str, Any]
     def __init__(self, type: builtins.type[Token], **attributes: Any):
         """
         :param type: The type of token this production will express
@@ -145,7 +145,7 @@ def grouping_mode(self, production: Production) -> bool:
             case ReferenceProduction() | TokenProduction(): return False
             case _:
                 raise ValueError
-    def combined(self, productions: Iterable, combinator: str) -> Iterable[str]:
+    def combined(self, productions: Iterable[Production], combinator: str) -> Iterable[str]:
         it = (self.format(production) for production in productions)
         yield from next(it)
         for item in it: