feat(sdk-coin-sui): fee payer signing support

[abhishekagrawal080]

This change allow sponsor/fee address signing in case of sui, currently sui fee amount is paid from sender address so there was no need set fee address and fee signature, but for new sponsored transaction we will provide fee adress and fee signature as well

TICKET: WIN-6028

[Copilot]

Pull Request Overview

This PR introduces fee payer (sponsor) signing support for Sui transactions, allowing gas fees to be paid by a third party rather than the transaction sender. This implements a gas tank pattern where a sponsor can cover the transaction costs.

• Adds fee payer signature handling in transaction builders and core transaction classes
• Introduces sponsor field to gas data configuration for identifying the fee payer
• Updates broadcast functionality to handle transactions with multiple signers (sender + fee payer)

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
test/unit/transactionBuilder/feePayer.ts	Comprehensive test suite for fee payer functionality including success and failure scenarios
src/sui.ts	Updates broadcast logic to handle transactions with fee payer signatures
src/lib/utils.ts	Adds utility method for executing transactions with multiple signers
src/lib/transferBuilder.ts	Integrates fee payer signature handling in transfer transaction builds
src/lib/transactionBuilder.ts	Core fee payer signing logic and sponsor validation
src/lib/transaction.ts	Fee payer signature storage, serialization, and broadcast format updates
src/lib/tokenTransferBuilder.ts	Integrates fee payer signature handling in token transfer builds
src/lib/mystenlab/builder/TransactionDataBlock.ts	Adds sponsor field support to gas configuration schema
src/lib/iface.ts	Defines GasData interface with optional sponsor field
src/lib/customTransactionBuilder.ts	Integrates fee payer signature handling in custom transaction builds

[Copilot]

There's a typo in the title: 'sigining' should be 'signing' in the PR title.

[Copilot]

The signImplementation method has been modified to duplicate signing logic that already exists in the Transaction.sign() method. This creates code duplication and potential maintenance issues. Consider calling this.transaction.sign(signer) instead of reimplementing the signing logic.

Suggested change

	const signable = this.transaction.signablePayload;
	const signature = signer.signMessageinUint8Array(signable);
	const signatureBuffer = Buffer.from(signature);
	this.transaction.addSignature({ pub: signer.getKeys().pub }, signatureBuffer);
	this.transaction.setSerializedSig({ pub: signer.getKeys().pub }, signatureBuffer);
	this.transaction.sign(signer);

[Copilot]

The addSignature method now calls setSerializedSig, but this creates a dependency where addSignature must always be called after setSerializedSig is available. This could cause issues if the calling order changes. Consider whether this logic belongs in addSignature or if the serialization should be handled separately.

Suggested change

	this.setSerializedSig(publicKey, signature);
	this.serialize();
	// Serialization should be handled separately after adding the signature.

[Copilot]

The toBroadcastFormat method now returns JSON instead of the previous string format. This appears to be a breaking change that could affect existing consumers of this API. Ensure this change is intentional and properly documented as a breaking change.

[Copilot]

[nitpick] The executeTransactionBlockWithMultipleSigners method creates an array and then immediately passes it to executeTransactionBlock. This adds unnecessary complexity. Consider simplifying the logic or making the conditional behavior more explicit.

Suggested change

	const signatures = feePayerSignature ? [senderSignature, feePayerSignature] : [senderSignature];
	return this.executeTransactionBlock(url, serializedTx, signatures);
	if (feePayerSignature) {
	return this.executeTransactionBlock(url, serializedTx, [senderSignature, feePayerSignature]);
	} else {
	return this.executeTransactionBlock(url, serializedTx, [senderSignature]);
	}

[balakrishna507]

are we going to stick with this transaction type, or create a new one?

[abhishekagrawal080]

we will create new one in another ticket

[krupanand-bitgo]

Please update ticket and PR descriptions for better clarity and easier review.

[abhishekagrawal080]

Please update ticket and PR descriptions for better clarity and easier review.

sure will add more details