Aioredis-cluster

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* fix problem when RedisConnection was GC collected after unhandled `asyncio.CancelledError`
* fix default `db` argument for pool/connection in cluster mode

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* (revert) apply cluster state only if cluster metadata is changed

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* fetch several cluster state candidates from cluster for choose best metadata for final local state
* apply cluster state only if cluster metadata is changed
* FIX: handle closed pubsub connection before gc its collected that trigger `Task was destroyed but it is pending!` message in log
* improve logging in state loader

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* fix bug when `ConnectionsPool.acquire()` is stuck because closed PUB/SUB connection is not cleanup from `used` set
* fix `ConnectionsPool.acquire()` incorrect wakeup order for connection waiters when connection is released
* `ConnectionsPool.execute()` now acquire dedicate connection for execution if command is blocking, ex. `BLPOP`
* `ConnectionsPool.execute()` now raises `ValueError` exception for PUB/SUB family command
* In `ConnectionsPool` PUB/SUB dedicated connections now is closing on `close()` call
* add `aioredis_cluster.abc.AbcConnection` abstract class
* add property `readonly` and method `set_readonly()` for `aioredis_cluster.abc.AbcConnection` and `aioredis_cluster.abc.AbcPool`
* `aioredis_cluster.Cluster` now require `pool_cls` implementation from `aioredis_cluster.abc.AbcPool`
* add `ssl` argument for factories `create_cluster`, `create_redis_cluster` and `Cluster` constructor
* add 10% jitter for cluster state auto reload interval
* fix incorrect iterate free connections in `select()`, `auth()` methods for `ConnectionsPool`

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* include `aioredis==1.3.1` source code into `aioredis_cluster._aioredis` and introduce `aioredis_cluster.aioredis` but for compatible and migration period
* this release have not backward incompatible changes
* __DEPRECATION WARNING:__ you must migrate from `import aioredis` to `import aioredis_cluster.aioredis` because `aioredis_cluster` starts vendorize `aioredis` package and maintain it separately. Using `aioredis` package __will be removed in v3__
* fix reacquire connection in `aioredic.ConnectionsPool` after Redis node failure

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* Add `xadd_620` commands method for support `XADD` options for Redis 6.2+