pevm: support parallel merge mode

[welkin22]

Description

Currently, in our PEVM code, only the execution phase is parallelized. After the parallel execution ends, the results need to be merged serially into the StateDB. I have modified the merging process to be executed in parallel as well, which further improves the performance of the PEVM and reduces the time consumption.

Rationale

By providing a new ParallelStateDB to replace the original StateDB, it supports concurrent reading and writing of data.
Provide ParallelGasPool instead of the original GasPool to support gas calculation in a concurrent environment.
Other similar changes.

Example

Enable parallel merge mode by adding startup parameters:

--parallel.parallel-merge

Note that this startup parameter conflicts with parallel.unordered-merge, and when both are set, parallel.unordered-merge will be invalid.

Changes

Notable changes:

• ParallelStateDB
• ParallelGasPool
• The state.StateDBer interface replaces direct references to StateDB.
• I supplemented a large number of txDAG files for the TestBlockchainWithTxDAG unit test. I found that the previous unit test had issues, as the code did not enter the branch that uses the DAG files.