fix(storage): replace imms with merged imms in any position of staging

[wenym1]

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What's changed and what's your intention?

Fix #14743
Fix #14724

In this PR, in the HummockReadVersion, we will not distinguish between imms and merged_imms. All imms will be in a single queue. A MergedImm version update will not require that the input imms are a suffix of the staging imm list, but only requires that they are consecutive in the staging imm list, and when applying the version update, such consecutive range of list will be replaced by output merged imm.

Some sanity check and logs are added by the way.

Checklist

• I have written necessary rustdoc comments
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[hzxa21]

Let's add a UT to cover #14743 (maybe via pushing events to event handler)

[wenym1]

Let's add a UT to cover #14743 (maybe via pushing events to event handler)

Unit test added

[hzxa21]

LGTM! Thanks for the quick fix.