Follow up of AcalaUncheckedExtrinsic

[xlc]

Follow up #1423

• More unit tests
• Verify every single byte in the transaction is covered by signature

• Acala/primitives/src/unchecked_extrinsic.rs

  Line 126 in 4e1f574

  let msg_hash = msg.hash(); // TODO: consider rewirte this to use `keccak_256` for hashing because it could be faster

• Acala/primitives/src/unchecked_extrinsic.rs

  Line 215 in 4e1f574

  // TODO: do the hash at compile time

• Acala/runtime/mandala/src/lib.rs

  Lines 1903 to 1904 in b69a220

  	// TODO: this is a hack access private nonce field
  	// remove this after https:/paritytech/substrate/pull/9810

[zjb0807]

Acala/primitives/src/unchecked_extrinsic.rs

Line 126 in 4e1f574

let msg_hash = msg.hash(); // TODO: consider rewirte this to use `keccak_256` for hashing because it could be faster

The hash of keccak_256 has been used here, so should not be needed here.

https:/rust-blockchain/ethereum/blob/145923737eedb053405a8bd0a8dd72e6bc446f14/src/transaction.rs#L204

[xlc]

Keccak256::digest does the hash in wasm runtime, but keccak_256 does the have in native so could be faster. But there is overhead of crossing wasm boundary so it may end up faster or slower. That's why we need to benchmark to decide which one is better.

[zjb0807]

paritytech/substrate#10835