Added a new API debug.getModifiedStorageNodesByNumber

[ehnuje]

Proposed changes

• Added a new debug API, debug.getModifiedStorageNodesByNumber(contractAddr, startBlockNum, endBlockNum, returnDiffList) to track the modified contract storage trie nodes between the two blocks specified.
• endBlockNum can be omitted and if so, the difference between the startBlockNum-1 and startBlockNum will be calculated.
• returnDiffList can be omitted and if so, the list of the changed nodes will be only printed to the log, not to the console. If it is entered as true, the list of the nodes will be also printed to the console.

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Further comments

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[aidan-kwon]

LGTM except for a minor thing