Problem: MultiStore interface is bloated

[yihuang]

Solution:

• Split out specialied methods from it, keeping the MultiStore generic

Description

Closes: #XXXX

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Author Checklist

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• included the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
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• provided a link to the relevant issue or specification
• reviewed "Files changed" and left comments if necessary
• included the necessary unit and integration tests
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• confirmed the correct type prefix in the PR title
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• reviewed state machine logic, API design and naming, documentation is accurate, tests and test coverage