feat(sdk-coin-sui): add fundsInAddressBalance support to StakingBuilder (AddStake)

[abhijit0943]

What

• Added fundsInAddressBalance(amount: string) method to StakingBuilder so wallets holding only address-balance SUI can stake
• When fundsInAddressBalance > 0, AddStake PTB inserts redeem_funds(SUI) + mergeCoins(gas, [addrCoin]) before splitCoins + request_add_stake
• StakingTransaction.toJson() now emits fundsInAddressBalance (from tx.expiration ?? { None: null } and tx.fundsInAddressBalance); getTxData() handles BalanceWithdrawal inputs and uses tx.expiration ?? { None: null }
• StakingBuilder.initBuilder() restores _fundsInAddressBalance from deserialized BalanceWithdrawal input and restores _expiration if ValidDuring
• StakingBuilder.buildSuiTransaction() passes expiration: this._expiration through to the returned SuiTransaction
• Fixed utils.getStakeRequests() to only parse MoveCalls ending with ::sui_system::request_add_stake, preventing crash on redeem_funds MoveCall (no arguments[2])
• Fixed utils.getWalrusStakeWithPoolRequests() with same target filter (::staking::stake_with_pool) for defensive parity
• Fixed WalrusStakingBuilder to use WalrusStakingTransaction instead of StakingTransaction (fixes loadInputsAndOutputs calling the correct getWalrusStakeWithPoolRequests)
• Removed now-unused StakingTransaction import from walrusStakingBuilder.ts

Why

• Wallets holding only address-balance SUI (no Coin<SUI> objects) cannot stake because StakingBuilder sourced the stake amount exclusively from gas coin objects. This mirrors the fundsInAddressBalance path in TransferBuilder Path 2c.
• StakingTransaction.toJson()/getTxData() previously hardcoded expiration: { None: null } — this would silently discard any ValidDuring expiration set by WP for Case 2 (addr-bal-only, empty gasData.payment). Fixed to use tx.expiration ?? { None: null }.
• The getStakeRequests bug would cause a runtime crash when parsing a staking transaction that includes a redeem_funds MoveCall (no arguments[2]).

Test plan

• New fundsInAddressBalance suite: mixed coin-objects + addr-bal command sequence, round-trip deserialization, multi-stake, default behavior unchanged
• New Case 2 test: fundsInAddressBalance > 0 + gasData.payment = [] (addr-bal-only stake)
• All 6 existing Sui Staking Builder tests still pass
• All Walrus Staking Builder tests pass (fixed regression from getStakeRequests target filter)
• 148 tests passing, 2 pre-existing failures unrelated to this change

Ticket: SI-1053

[linear-code]

SI-1053