refactor: change the inner type of Hex

[KaoImin]

What this PR does / why we need it?

Change the inner type of Hex to Bytes with the following advantages:

1. Half memory cost.
2. No error handling.
3. Cloning bytes::Bytes is very cheap.

What is the impact of this PR?

No Breaking Change

PR relation:

• Ref Store bytes in memory rather than hex string #1365

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• OCT 6-10
• OCT 11
• OCT 16-19
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[axon-bot]

CI tests run on commit:

• commit id: edf04c9

CI test list:

• OCT 1-5 And 12-15
• v3 Core Tests
• Web3 Compatible Tests

Please check ci test results later.

[yangby-cryptape]

I prefer the current method of handling hex strings.

Also, I have to point that:

• The serde deserialization is changed.

  • Previous is not strict with 0x prefix.

  • Current is strict with 0x prefix; no-prefix or 0X prefix is not acceptable.

• But the from_string and decode is still not strict with 0x prefix.

There should be only one rule for hex conversion to reduce ambiguity.

p.s. I prefer to use the strict method, but I don't persist in.

[KaoImin]

/run-ci

[blckngm]

Nit: it's a bit more idiomatic to use parse instead of from_str directly.

[axon-bot]

CI tests run on commit:

• commit id: 0526fd7

CI test list:

• OCT 1-5 And 12-15
• v3 Core Tests
• Web3 Compatible Tests

Please check ci test results later.

[KaoImin]

/run-ci

[axon-bot]

CI tests run on commit:

• commit id: 010f6a4

CI test list:

• OCT 1-5 And 12-15
• v3 Core Tests
• Web3 Compatible Tests

Please check ci test results later.