no-transform has no arguments as a request or response directive (RFC
9111). Prior to this fix, cc.no_transform would return None whether the
directive is present or not.

The type for this property is `int | None`, so getting `"*"` for a
malformed directive is surprising. I think dropping the empty value here
is better than fixing the type.

- cache_control_property with type=bool never return None
- some non-bool types were marked as returning bool instead of str
- max_stale can return "*" in addition to int or None

mypy doesn't use the type of setters as of 1.9.0 (see python/mypy#3004),
but I think it's still good to have these be accurate (maybe the other
type checkers work better here).

mypy's recommendation is to use `# type: ignore` comments if setter
types don't match getters, which you see when setting no_cache to True.