fix: make `hscan` return flat list of entries

[silverwind]

Fixes: https://github.com/stipsan/ioredis-mock/issues/962 Ref: https://redis.io/commands/scan/#return-value

HSCAN [returns an] array of elements contain two elements, a field and a value, for every returned element of the Hash.

[github-actions[bot]]

:tada: This PR is included in version 8.8.2 :tada:

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