refactor: slightly improve security for secret keys

[yangby-cryptape]

What this PR does / why we need it?

• Keep a human-readable string of a private key is very dangerous.

• Do not copy private keys again and again.

• If the memory of a private key is not zeroized after the key dropped, it could be read from other threads and other processes.

  Also, that piece of memory could be read by programs started after axon stopped.

• Remove unnecessary unwrap() and structs conversions.

  +---------------+
  |  Secret Key   |
  | (Hex String)  |    +----------------------------------------------------------------+
  +---------------+    |                                                                |
         |             |             This PR deleted these useless conversions.         |
         v             |                                                                |
  +---------------+    |     +---------------+      +--------+      +--------+          |
  |  Secret Key   |  Clone   |  Secret Key   |----->| Secret |----->| Public |          |
  |    (Bytes)    |--------->|    (Bytes)    |      |   Key  |      |   Key  |          |
  +---------------+    |     +---------------+      +--------+      +--------+          |
         |             |                                                |               |
         v             |                                                v               |
     +--------+        |                         +--------+      +------------+         |
     | Secret |        |               +---------| Public |<-----| Public Key |         |
     |   Key  |        |               |         |   Key  |      |   (Bytes)  |         |
     +--------+        |               |         +--------+      +------------+         |
         |             +---------------|------------------------------------------------+
         v                             v
     +--------+                  +------------+
     | Public |- - - - - - - - ->| Public Key |
     |   Key  |  This PR Added   |   (Bytes)  |
     +--------+                  +------------+
        |                              |
        v                              v
    +----------+                 +----------+
    |   Node   |<----------------| Address  |
    |   Info   |                 |          |
    +----------+                 +----------+
  

What is the impact of this PR?

No Breaking Change

CI Settings

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• OCT 6-10
• OCT 11
• OCT 16-19
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CI Description

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[axon-bot]

CI tests run on commit:

• commit id: 09a12ae

CI test list:

• Code Format
• E2E Tests
• OCT 1-5 And 12-15
• OCT 6-10
• OCT 11
• OCT 16-19
• v3 Core Tests
• Web3 Compatible Tests

Please check ci test results later.