Added timeoutPerRequest option

[mjomble]

Closes #61

Based on the fact that this feature was discussed back in 2015 (#61) and is still not implemented, I'm assuming the implementation in this PR is a very naive one and there's a bunch of special cases it's not covering. But maybe it can still get the ball rolling 🙂

@luin you've said that "It's not easy to support timeoutPerRequest option efficiently". Could you elaborate on this?
Is setTimeout inefficient? Or would we need to add a bunch of additional logic to this PR that would slow things down?

[luin]

you've said that "It's not easy to support timeoutPerRequest option efficiently". Could you elaborate on this?

Hmm...good question. I thought having hundreds of timers would cause performance impact, but seems it isn't the case. Another reason I didn't add this feature was I thought it could be easily implemented on client side via ex Promise.race, and I didn't want to mislead users to think that the timeout was applied on the server side (like a Lua script can't be interrupted if it timed out). However, as users pointed out that if they used third-party libraries they won't be able to wrap Promise.race so it may be worth to add this feature.

[mjomble]

I now noticed that the other timeout options follow a consistent naming pattern:

• connectTimeout
• disconnectTimeout
• slotsRefreshTimeout

so I renamed this option to commandTimeout.
I also added a sentinelCommandTimeout option that's passed on to the internally created Redis client for sentinels.

I've also documented commandTimeout, but I noticed that no sentinel-specific options have currently been documented, so I left sentinelCommandTimeout undocumented for now. Perhaps the sentinel options could be documented all at once in a separate PR.

[ioredis-robot]

🎉 This PR is included in version 4.25.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[luin]

Awesome! Great work Andres!

[varungbt]

From the code I see that when a command timeout occurs, the promise is rejected. Is there a way to listen for command timeout events?