Minor API pain-points

These are things that are easy to workaround downstream, but would one-liner if we had upstream support. I will update the list as I find more things:
1) Direct API for calculating assetid and token id directly from prevouts during initial issuance. This currently a multi step process which requires dealing calling the AssetId::generate_asset_entropy() API.
2) Display implementations of Explicit Asset should add the 0x01 prefix
3) Add FromStr implementation for confidential::Asset/Value/Nonce. Currently, we need to decode a bytes and call `encode::deserialize`. It would be great to have methods for a) from_slice/to_vec() b) Display/FromStr c) FromHex/ToHex.
4) Implement auto-derives for Error data structures. For example: `UnBlindError`.
5) Separate out TxOut::unblind API into two APIs. TxOut::unblind_from_prf. This will also it to re-use it for psbt logic too

首先閱讀列出的 AssetId::generate_asset_entropy()、Explicit Asset Display、confidential::Asset/Value/Nonce、UnBlindError 和 TxOut::unblind 入口點。這個 issue 將五個獨立的 API 請求歸在一起，因此首先要將它們分開，並對照現有的 Rust 交易與 PSBT 程式碼界定各自的範圍。完成的標準是：針對選定的請求，已有一致同意的範圍和相應的實作，且其行為由專案現有的檢查涵蓋。

由索引模型根據 Issue 內容生成。