Cache expirations

[cicdw]

Closes #13865

This PR wires up cache expirations by storing an optional expiration timestamp within the PersistedResultBlob that we write to the result store.

[desertaxle]

LGTM! Just one nit/question on typing.

[desertaxle]

nit: value doesn't necessarily need to be a BaseResult right? I find I'm able to stage arbitrary values with the transaction context manager:

from prefect.transactions import transaction


def main():
    with transaction(key="static") as txn:
        if txn.is_committed():
            return txn.read().get() # need .get because txn.read() returns a result
        else:
            value = {"x": 1}
            txn.stage(value)
            return value


if __name__ == "__main__":
    print(main())

That script will print {"x": 1} even if I change value on a subsequent run.

[cicdw]

So it's tricky - for the full lifecycle to truly work properly, I do think the record stores should always interact via result payloads. However, that being said, I think the stage -> write functionality will work just fine without staging a true "Result". I changed this type because the moment we use a different record store type (such as Redis), we'll need to persist a serialized Result payload into the record store, which presupposes the value is a prepared result. That probably is a little convoluted, but basically what I'm saying is that right now it works fine because we're overloading the Result interface, but this distinction will become important when we decouple.