[BUG] Duplicated arguments are accepted in ZINTER, ZUNION, and ZDIFF command about valkey HOT 4 OPEN

@madolson do you think it is a bug?

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I think streams command argument parser is written in a similar manner, where the last argument is picked.

@yyyhe Is that an accidental behavior by the client/yourself of passing the same argument multiple times?

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I think it's a minor bug, since we aren't conforming to the documented behavior. We had a very similar issue related to 'hello' in the past (you can pass 'auth' multiple times), which I think just low quality argument parsing. I think it's worth trying to clean an up the argument parsing in the next major version.

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Here we have an interesting piece of history, which we have discussed many times in the past (I will not quote the issues from Redis here). There are two scenarios:

1. For conflicting or semantically opposite arguments, Valkey rejects such usage, for example, SET key value xx nx would directly return an error.

2. As for arguments of the same type, Valkey currently adopts a 'last win' strategy.

The core issue here is the second point, regarding the same arguments. Honestly, I'm not a fan of the 'last win' strategy, it's not a good usage pattern (I suspect that initially using multiple arguments might have likely been a user error). But indeed, there are quite a few users who use it this way. Although we have the opportunity to make some breaking changes in the next major version, we need to be very cautious, because this kind of usage is hard for users to detect themselves and it's difficult to carry out a comprehensive check before upgrading to a major version, which can lead to crash after the upgrade.

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