Some of the results of blockchain.*.unpack is inconsistent with api.*

[homura]

          Thanks for your PR. However, I have noticed that the `blockchain.Transaction.unpack` function behaves differently from `api.Transaction`. The `blockchain` module directly uses number codecs, which results in the unpacked output being either a `number` or a `BI`. Ideally, any type of number should be in `string(hex formatted)`. This inconsistency was not caused by your PR, but by your comment "cannot set number 0 to call pack", which drew my attention to it. To address this issue, Lumos may have to modify the `blockchain.*.unpack` function to output a `string(hex format)` instead of a `number`.

Originally posted by @homura in #599 (comment)