fix(hardfork): built-in miner shouldn't ignore the extension field in block templates

[yangby-cryptape]

Issue

The built-in miner will ignore the extension field in block templates.

Reason

When call as_builder() to convert a Block to a BlockBuilder, all extra fields will be ignored, because the generated code of BlockBuilder couldn't know any about extra fields.

And the extension field is an extra field on the molecule-serialized struct Block, it will be ignored, too.

Solution

We already have the advanced Block builder, which is not generated.

The as_advanced_builder will handle the extension field.

How to reproduce the issue and test the solution?

• Set the extension in the TxPoolService::build_block_template(..) to the follow value:

  let extension = if candidate_number % 2 == 0 {
      let bytes: Bytes = format!("block number = {}", candidate_number).as_bytes().pack();
      Some(bytes.into())
  } else {
      None
  };

• Start a dev chain with func = "Eaglesong" and run a built-in miner.

• Check the extension field in all blocks.

[quake]

bors r=quake,zhangsoledad

[bors]

Build succeeded:

• ci