cleanup: fix typings for requirements_file.py

[shubhbapna]

part of #226

Fixes the following errors:

src/fromager/requirements_file.py:29: error: Missing type parameters for generic type "dict"  [type-arg]
src/fromager/requirements_file.py:38: error: List comprehension has incompatible type List[dict[str, object]]; expected List[Environment]  [misc]
src/fromager/requirements_file.py:41: error: Argument 1 to "evaluate" of "Marker" has incompatible type "Environment"; expected "dict[str, str] | None"  [arg-type]

Need this to fix errors in dependencies.py but I am not combining the two together in one PR because dependencies.py has a lot of typing fixes