Add the support of the BLMPOP command

[HolyLow]

This closes #1522.

This PR moves all the blocking-event related code to a upper class BlockedPopCommand, as all the blocking commands would share these utils.
If the BlockedPopCommand design gets accepted, I would try to refactor the other blocking commands, such as BLPOP, BRPOP and BLMOVE to reduce the code redundancy, just as commented by @git-hulk in previous discussion.

Any suggestions are welcomed.

[PragmaTwice]

Hi @HolyLow , thank you for your contribution.

Could you consider to rewrite it in our new helper class BlockingCommander?

You can refer to CommandBPop for how to use it.

[HolyLow]

@PragmaTwice seems we've done the same thing separately... Sure, I would refactor the code. As the design is very similar, it wouldn't take long.

[HolyLow]

@PragmaTwice refactored to use BlockingCommander.

[HolyLow]

@PragmaTwice A CI test case failed with Ubuntu 20.04, clang, TLS on. The test case is in the tls_test (no command logic involved?), and I try my best to try to reproduce the problem on my local environment (Ubuntu22.04, clang-16, TLS on), but the error could not be reproduced...

I'm not aware what I should do now, could you please help?

[git-hulk]

@PragmaTwice A CI test case failed with Ubuntu 20.04, clang, TLS on. The test case is in the tls_test (no command logic involved?), and I try my best to try to reproduce the problem on my local environment (Ubuntu22.04, clang-16, TLS on), but the error could not be reproduced...

I'm not aware what I should do now, could you please help?

It's a flaky test case, can ignore this failure for now. We're still investigating.

[git-hulk]

LGTM