wallet: importdescriptors should output the request on error #35224

Waiting for #35185 to be merged so I can rebase on it

Motivation

I was motivated by this comment #35185 (comment) because when using the importdescriptors rpc on error we should get a more descriptive error message than Missing required timestamp field for key. This is because multiple descriptors could be imported, and it would be useful to know the exact request that failed.

Solution

Instead of just printing a static error message, Missing required timestamp field for key also output the exact request that failed.

Example

Request

[
  {
    "desc": "wpkh([abcd1234/84h/1h/0h]tpub.../0/*)#x9abc123",
    "timestamp": 1710000000,
    "active": true,
    "range": [0, 100]
  },
  {
    "desc": "wpkh([abcd1234/84h/1h/0h]tpub.../1/*)#y8def456",
    "timestamp": "now",
    "internal": true,
    "active": true,
    "range": [0, 100]
  },
  {
    "desc": "pkh(039dcc64c5c644baf0145a5f7322b16399a01a0ee2a182e3150946fe7946358247)#68u5tv65",
    "active": false
  }
]

Before

{
  "code": -3,
  "message": "Missing required timestamp field for key"
}

After

{
  "code": -3,
  "message": "Missing required timestamp field for import request: {\"desc\":\"pkh(039dcc64c5c644baf0145a5f7322b16399a01a0ee2a182e3150946fe7946358247)#68u5tv65\",\"active\":false}"
}

Note: after #35185 is merged, the output will be per item.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35224.

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