feat(sdk-coin-ton): add setFullWithdrawalMessage() via w comment to SingleNominatorWithdrawBuilder

[bitgo-ai-agent-dev]

Summary

Implements the full-withdrawal path for TON single nominator contracts (orbs-network/single-nominator), resolving ST-802.

The single nominator contract supports a text comment "w" that drains balance - gas - MIN_TON_FOR_STORAGE automatically. This PR adds setFullWithdrawalMessage() to SingleNominatorWithdrawBuilder, mirroring the existing TonWhalesWithdrawalBuilder.setFullWithdrawalMessage().

Changes

• constants.ts: Add SINGLE_NOMINATOR_WITHDRAW_ALL_COMMENT = 'w'
• iface.ts: Add isFullUnstake?: boolean to TxData interface
• transaction.ts: Add isFullUnstake field to Transaction, expose in toJson(), load in fromRawTransaction(), detect "w" comment in parser to set SingleNominatorWithdraw type and isFullUnstake = true
• singleNominatorWithdrawBuilder.ts: Add setFullWithdrawalMessage() — sets isFullUnstake = true and message = 'w'
• test/unit/singleNominatorWithdrawBuilder.ts: Add test cases for full withdrawal build and round-trip

Usage

// Partial (existing)
builder.setWithdrawAmount('500000000000').setWithdrawMessage();

// Full (new)
builder.setFullWithdrawalMessage();
// → plain transfer with text comment "w"

Test plan

• Full withdrawal builds a SingleNominatorWithdraw tx with isFullUnstake = true
• Transaction round-trips correctly (build → parse → rebuild → same bytes)
• Signed transaction round-trip preserves signatures
• Existing partial withdraw tests unaffected

🤖 Generated with Claude Code

[linear]

ST-802 [BitGoJS] TON Single Nominator: add setFullWithdrawalMessage() via "w" comment