Update gateway HTTP server object mapping format

[teor2345]

This PR makes the gateway use the same object mapping format as the RPC server subscription. This is a breaking change.

The format is documented here (it's the same as the result inside the subscription wrapper):
https://github.com/autonomys/subspace/tree/main/crates/subspace-gateway-rpc#using-the-gateway-rpcs

As part of this change, the gateway:

• retrieves batches of mappings via RPC and HTTP. HTTP uses a + separator if there is more than one mapping. (Preparation for Re-use downloaded pieces in subspace-gateway  #3316.)
• does the hash checks during object retrieval. (Preparation for Reduce the number of pieces downloaded by the object fetcher in subspace-gateway #3318.)
• simplifies the RPC and HTTP code. (Preparation for Merge http and rpc commands in subspace-gateway #3317.)

I also made the logging inside the object fetcher more consistent.

Close #3323.

Code contributor checklist:

• I have read, understood and followed contributing guide

[nazar-pc]

This would work, but why can't we just make a breaking change here? Is anyone except us using gateway? Can't they change the way they send data when upgrading gateway backend at once?

[teor2345]

This would work, but why can't we just make a breaking change here? Is anyone except us using gateway? Can't they change the way they send data when upgrading gateway backend at once?

@clostao are you happy to just make a breaking change here? It would be simpler for us.

If we did it that way, next time you upgraded the gateway, you'd also need to upgrade to a version of the indexer which sent block numbers as integers (rather than block number strings).

[clostao]

No problem with that

[teor2345]

If we did it that way, next time you upgraded the gateway, you'd also need to upgrade to a version of the indexer which sent block numbers as integers (rather than block number strings).

We also wanted to make breaking changes to allow batch retrieval of mappings, so we can cache pieces and use them with multiple mappings. So I made all those breaking changes in this PR.

The gateway and indexer request formats are compatible with the existing format. If you want to support multiple hashes, they can be fetched as /{objects|data}/hash1+hash2+hash3. (Single hashes are still just /{objects|data}/hash.)

The indexer response format was:

{
  "hash": "0000000000000000000000000000000000000000000000000000000000000000",
  "pieceIndex": 0,
  "pieceOffset": 0,
  "blockNumber": 0
}

And it's now the same format as the inner part of the RPC subscription. It's more compact to support batches (piece index is first, followed by piece offset), with a version to support future format changes:

{
  "blockNumber": 0,
  "v0": {
    "objects": [
      [
        "0000000000000000000000000000000000000000000000000000000000000000",
        0,
        0
      ]
    ]
  }
}

If that's too much change, let me know, and we'll work out how to do it in stages.

[teor2345]

@clostao just checking these changes work for you?

[clostao]

Looks good to me

[nazar-pc]

Should be &[PieceIndex] in such cases

[teor2345]

Yeah I tried that and something weird happened with type inference. Happy to have another go next time around.