fix: fix concurrent pipeline invocation results

[yahiro07]

This PR fixes mixed response problem for parallel pipeline calls.

I made the modification so as the pipeline calls queued in the same way as regular commands.
To achieve this, the type of command queue item has changed to hold a general lambda function.

In my previous branch (yahiro07:pipeline-parallel-execution), there is a problem it doesn't work with Redis 6.
In this branch (yahiro07:pipeline-parallel-execution-2), I confirmed it works with both Redis 6 and Redis 7.

Please check:

• The test fails if you only add the test code.
• The test passes if you apply whole changes.

Closes #427

[uki00a]

@yahiro07 LGTM and thanks! 👍 v0.32.2 has been released which includes this fix.

[yahiro07]

Thank you!