Return a result from IO operations

[d-v-b]

As mentioned in #3748, our IO operations look like this:

def get(key) -> payload | None: ...
def set(key) -> None: ...

There's a similar story for the CodecPipeline class which has its own, slightly different IO API.

Practically this means we are throwing away a lot of useful information about each IO operation, such as how long these operations took, as well as store-specific metadata like http status codes.

Here is a proposed minimal API:

class GetResult(TypedDict):
  key: str
  duration: float
  status: Literal["success", "missing"]
  payload: NotRequired[bytes]

class SetResult(TypedDict):
  """TBD"""
   key: str
   duration: float

def get(key) -> GetResult: ...
def set(key) -> SetResult: ...

Our stores are all capable of giving us this information. We should probably use it.