PRE should work with privatekey also

at the moment, PRE works with mnenomics only. It should also work with private keys also.

steps to reproduce:

1. from wallet1.json share any encrypted to wallet2.json

if wallet2.json has mnemonics in it. Then wallet2.json will be able to download the shared file.

But if the wallet2.json has mnemonics then they get error.

https://github.com/0chain/gosdk/assets/9148277/65611ce2-13c6-41b9-97d7-bb1337b3804a

查看 gosdk 中的 PRE（代理重加密）實作，很可能在與錢包或加密相關的檔案中。問題是當前只有基於助記詞的錢包可以解密共享檔案；基於私鑰的錢包會失敗。首先找到檔案共享/解密邏輯處理錢包憑證的位置。檢查所提供影片中的錯誤以了解不匹配的原因。透過建立兩個錢包（一個使用助記詞，一個使用私鑰）進行測試，並追蹤解密流程。

由索引模型根據 Issue 內容生成。