Add test for negative transaction version w/ CSV to tx_valid.json #29291

This PR adds a static test vector corresponding to the bug found in various implementations of the bitcoin protocol discovered by dergoegge

For more information see:

https://delvingbitcoin.org/t/disclosure-btcd-consensus-bugs-due-to-usage-of-signed-transaction-version/455

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ACK 97181decf5726aab6c5cd01b3e1964072f2531ff

ACK 97181decf5726aab6c5cd01b3e1964072f2531ff

ACK. Somewhat surprisingly, decoderawtransaction is showing a positive version number:

% ./src/bitcoin-cli decoderawtransaction "ffffffff01000100000000000000000000000000000000000000000000000000000000000000000000030251b2010000000100000000000000000000000000"
{
  "txid": "d3230b80abeab3cf6c1c0f1c55c3694545146b1936348476bf3646276af83d38",
  "hash": "d3230b80abeab3cf6c1c0f1c55c3694545146b1936348476bf3646276af83d38",
  "version": 4294967295,
  "size": 63,
  "vsize": 63,
  "weight": 252,
  "locktime": 0,
  "vin": [
    {
      "txid": "0000000000000000000000000000000000000000000000000000000000000100",
      "vout": 0,
      "scriptSig": {
        "asm": "-12881",
        "hex": "0251b2"
      },
      "sequence": 1
    }
  ],
  "vout": [
    {
      "value": 0.00000000,
      "n": 0,
      "scriptPubKey": {
        "asm": "",
        "desc": "raw()#58lrscpx",
        "hex": "",
        "type": "nonstandard"
      }
    }
  ]
}

There's this note in TxToUniv().

(Edit: pasted wrong terminal output)

ACK. Somewhat surprisingly, decoderawtransaction is showing a positive version number:

From 2019 onwards, bitcoind started to display transactions versions (on the RPC layer) as unsigned everywhere: #16525

Interestingly, prior to that in 2018, an attempt was made to do the same, but rejected under the basis that it's actually signed everywhere with one exception: #12430 (comment)

This bitcoind PR that merged was prompted by a rust-bitcoin issue pointing out they were using a u32 instead of a i32 for their transaction struct: https://github.com/rust-bitcoin/rust-bitcoin/issues/287