[cachetools] Support cache_info on functions

[brandonchinn178]

@ttl_cache()
def foo(x: str) -> int:
    ...

# "Callable[[Any, str], list[str] | None]" has no attribute "cache_info"
print(foo.cache_info())

Related: #11280 #6347

[srittau]

Currently, all the cachetools functions just return IdentityFunction. They should probably return a custom callable class with additional attributes, similar to what functools does.