feat: move PieceMetadata off-chain

[Kubuxu]

Due to gas costs, we are going to stop storing PieceMetadata on-chain.

In principle, the change is the removal of:

filecoin-services/service_contracts/src/FilecoinWarmStorageService.sol

Lines 841 to 859 in 54885b9

	for (uint256 k = 0; k < pieceKeys.length; k++) {
	string memory key = pieceKeys[k];
	string memory value = pieceValues[k];
	require(
	bytes(dataSetPieceMetadata[dataSetId][pieceId][key]).length == 0,
	Errors.DuplicateMetadataKey(dataSetId, key)
	);
	require(
	bytes(key).length <= MAX_KEY_LENGTH,
	Errors.MetadataKeyExceedsMaxLength(k, MAX_KEY_LENGTH, bytes(key).length)
	);
	require(
	bytes(value).length <= MAX_VALUE_LENGTH,
	Errors.MetadataValueExceedsMaxLength(k, MAX_VALUE_LENGTH, bytes(value).length)
	);
	dataSetPieceMetadata[dataSetId][pieceId][key] = string(value);
	dataSetPieceMetadataKeys[dataSetId][pieceId].push(key);
	}

plus depracation/removal of getters of PieceMetadata.
PieceMetadata will still be emitted as an event.

• Piece metadata stops being accessible on-chain synapse-sdk#917

[Kubuxu]

I'm considering adding a permissionless endpoint to remove old metadata off the chain to make cleanup easier for datasets that got terminated.

[Kubuxu]

Reopening for tracking tooling