add utxo split、merge、list

[superlitian]

Description

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Fixes # (issue)

Type of change

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• New feature (non-breaking change which adds functionality)

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[godeamon]

在转账接口的 option 增加一个 num 参数，split 和 merge 都是转账交易，在调用转账接口时，指定上这个可选参数，例如如果这个参数是0，就是普通转账，如果是1就是merge，大于1就是split。在转账接口的proposal实现部分判断这个参数，然后拼装交易的 utxo input 和 output。