Client: Merge Switch Hack for --dev Option

[holgerd77]

This is a small hack on the --dev option to create a network setup where a Merge HF is triggered and can be tested.

This produces the following chain configuration:

{
  name: 'devnet',
  chainId: 123456,
  networkId: 123456,
  genesis: {
    hash: '0x4c748ec987a50eb6d205c656984d12f6bb2495f8b17182309a4f984f7c938ad3',
    timestamp: '0x614b3731',
    gasLimit: 4700000,
    difficulty: '0x1',
    nonce: '0x0000000000000000',
    extraData: '0x0000000000000000000000000000000000000000000000000000000000000000c9c6d3296fddb75bfbe9855049de64ea0b0c27870000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
    mixHash: '0x0000000000000000000000000000000000000000000000000000000000000000',
    coinbase: '0x0000000000000000000000000000000000000000',
    stateRoot: '0x6c7b25b2e99a76e72af08c72fa94366c676237010aa3c7ca0ad50baed78c1d90'
  },
  bootstrapNodes: [],
  consensus: {
    type: 'poa',
    algorithm: 'clique',
    clique: { period: 10, epoch: 30000 }
  },
  hardforks: [
    { name: 'chainstart', block: 0, td: null },
    { name: 'homestead', block: 0, td: null },
    { name: 'tangerineWhistle', block: 0, td: null },
    { name: 'spuriousDragon', block: 0, td: null },
    { name: 'byzantium', block: 0, td: null },
    { name: 'constantinople', block: 0, td: null },
    { name: 'petersburg', block: 0, td: null },
    { name: 'istanbul', block: 2, td: null },
    { name: 'berlin', block: 4, td: null },
    { name: 'london', block: 6, td: null },
    { name: 'merge', block: null, td: 16 }
  ]
}

Mining is executed up till block 7 and then stops.

For testing purposes, do not merge.

[codecov]

Codecov Report

Merging #1510 (63c0873) into master (e897985) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

Flag	Coverage Δ
block	86.71% <ø> (+0.13%)	⬆️
blockchain	82.85% <ø> (+0.06%)	⬆️
client	83.02% <100.00%> (-0.20%)	⬇️
common	94.27% <ø> (ø)
devp2p	82.86% <ø> (-0.04%)	⬇️
ethash	90.76% <ø> (ø)
tx	87.34% <ø> (ø)
vm	79.38% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[ryanio]

by the way geth defines this as terminalTotalDifficulty not mergeBlock, I have implemented it here

[ryanio]

i also implemented stopping the miner, although I did it on chainCommon not execCommon - I believe execCommon should already work but I haven't implemented updating the chainCommon yet (will be doing that soon in my next work)

[ryanio]

this is outdated now, see the most recent merge PR for latest work