cmd/evm: add difficulty calculation to t8n tool

[holiman]

This PR adds functionality to the evm t8n to calculate ethash difficulty. If the caller does not provide a currentDifficulty, but instead provides the parentTimestamp (well, semi-optional, will default to 0 if not given), and parentDifficulty, we can calculate it for him.

The caller can also provide a parentUncleHash. In most, but not all cases, the parent uncle hash also affects the formula. If no such hash is provided (or, if the empty all-zero hash is provided), it's assumed that there were no uncles.

Documented in testdata/14/readme.md.

Closes #23249

Example run

[user@work evm]$ ./evm t8n --input.alloc=./testdata/14/alloc.json --input.txs=./testdata/14/txs.json --input.env=./testdata/14/env.json --output.result=stdout --state.fork=London
INFO [08-08|17:35:46.876] Trie dumping started                     root=6f0588..7f4bdc
INFO [08-08|17:35:46.876] Trie dumping complete                    accounts=2 elapsed="89.313µs"
INFO [08-08|17:35:46.877] Wrote file                               file=alloc.json
{
 "result": {
  "stateRoot": "0x6f058887ca01549716789c380ede95aecc510e6d1fdc4dbf67d053c7c07f4bdc",
  "txRoot": "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
  "receiptRoot": "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
  "logsHash": "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
  "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
  "receipts": [],
  "currentDifficulty": 3311729559732224
 }
}

[holiman]

@winsvega does this work for you?

[rjl493456442]

please gofmt it

[holiman]

@winsvega ping -- does this fit your needs?

[winsvega]

I guess. I can chek tomorrow.

[winsvega]

we used to treat every field as string.
the currentDifficulty is returned as int in json

like on the input:

{
  "currentCoinbase": "0xc94f5374fce5edbc8e2a8697c15331677e6ebf0b",
  "currentGasLimit": "0x750a163df65e8a",
  "currentBaseFee": "0x500",
  "currentNumber": "12800000",
  "currentTimestamp": "10015",
  "parentTimestamp" : "99999",
  "parentDifficulty" : "0x2000000000000"
}

this started because there was some team. like JS implementation and they complained that it is difficult to parse different types in test jsons. so we have all the types in jsons as string.

[holiman]

@winsvega fixed:

]$  ./evm t8n --input.alloc=./testdata/14/alloc.json --input.txs=./testdata/14/txs.json --input.env=./testdata/14/env.json --output.result=stdout --state.fork=London
INFO [08-25|11:30:17.118] Trie dumping started                     root=6f0588..7f4bdc
INFO [08-25|11:30:17.118] Trie dumping complete                    accounts=2 elapsed="85.624µs"
INFO [08-25|11:30:17.118] Wrote file                               file=alloc.json
{
 "result": {
  "stateRoot": "0x6f058887ca01549716789c380ede95aecc510e6d1fdc4dbf67d053c7c07f4bdc",
  "txRoot": "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
  "receiptRoot": "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
  "logsHash": "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
  "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
  "receipts": [],
  "currentDifficulty": "0xbc40020000000"
 }
}

[MariusVanDerWijden]

LGTM, just a tiny question