Apart from adding the missing coverage, this PR also adds `blockedBeforeSleep`
that gathers all block-related functions from `beforeSleep`
The order inside `blockedBeforeSleep` is different: now `handleClientsBlockedOnKeys`
(which may unblock clients) is called before `processUnblockedClients` (which handles
unblocked clients).
It makes sense to have this order.
There are no visible effects of the wrong ordering, except some cleanups of the now-unblocked
client would have happen in the next `beforeSleep` (will now happen in the current one)
The reason we even got into it is because i triggers an assertion in logresreq.c (breaking
the assumption that `unblockClient` is called **before** actually flushing the reply to the socket):
`handleClientsBlockedOnKeys` is called, then it calls `moduleUnblockClientOnKey`, which calls
`moduleUnblockClient`, which adds the client to `moduleUnblockedClients` back to `beforeSleep`,
we call `handleClientsWithPendingWritesUsingThreads`, it writes the data of buf to the client, so
`client->bufpos` became 0
On the next `beforeSleep`, we call `moduleHandleBlockedClients`, which calls `unblockClient`,
which calls `reqresAppendResponse`, triggering the assert. (because the `bufpos` is 0) - see https://github.com/redis/redis/pull/12301#discussion_r1226386716
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