Implement `@cached_many`

[eigenein]

Suggested use case:

@cached_many(cache)
def expensive_function(items: Iterable[K], …) -> Mapping[K, V]:
    …

expensive_function(["foo", "bar", "qux"], …)

Expected behaviour

expensive_function should get called only on items which aren't present in the cache. Pseudo-code:

cached_items = cache.get_many(*items)
new_items = wrapped_function(*(item for item in items if item not in cached_items), *args, **kwargs)
cache.set_many(new_items)
return {**cached_items, **new_items}

Discussion

• Should @cached_many allow specifying of the items parameter by index or keyword argument name?