fix: use dedicated address UTXO endpoint

[tolga-tom-nook]

Summary

• fixes Address.getAddressUTXO() to call /address/utxo/{address}
• avoids duplicating the unconfirmed-transactions endpoint for UTXO lookups
• adds a focused Jest regression test for the requested endpoint and returned data shape

Root cause / acceptance proof

On the upstream main branch, getAddressUTXO() calls the exact same endpoint as getUnconfirmedAddressTransactions():

/address/unconfirmed/transactions/${address}

That endpoint returns a paginated transaction-list shape, not UTXOs. The live API exposes a dedicated UTXO endpoint and returns a distinct UTXO shape:

GET /address/utxo/bgl1qlmzckh904vze03n0lwzptt5dkmvf2vj3ev4qm9
{"data": [{"txId": "10c84f22...", "vOut": 1, "block": 306435, "txIndex": 1, "amount": 633731214}], ...}

GET /address/unconfirmed/transactions/bgl1qlmzckh904vze03n0lwzptt5dkmvf2vj3ev4qm9
{"data": {"page": 1, "limit": 50, "pages": 0, "list": []}, ...}

Validation

• npx jest src/__tests__/address-utxo-endpoint.test.ts --runInBand --no-cache
• npx tsc -p tsconfig.json
• npm test -- --runInBand --no-cache

Test Suites: 6 passed, 6 total
Tests:       23 passed, 23 total

Bounty note

Submitting as a focused SDK correctness fix for the Bitgesell bounty/improvement program, especially BitgesellOfficial/bitgesell#81. If approved for payout, USDT/EVM-compatible address: 0x4a76c7E64C08cF29B59eFC640b4ada97A270d428.

Assisted by Hermes Agent.

[MyTH-zyxeon]

Maintainer review assist for the Bitgesell #81 improvement queue:

This PR looks like a focused SDK correctness fix: Address.getAddressUTXO() stops calling the unconfirmed-transaction list endpoint and now targets the dedicated /address/utxo/{address} route. The added Jest test is useful because it asserts the exact URL and returned UTXO shape instead of only proving that the method returns something.

Suggested merge checks:

• Run the focused address UTXO test and the existing SDK test suite so the endpoint regression stays covered alongside the older address methods.
• Confirm the SDK _get wrapper unwraps the API response envelope the same way the new test expects, since the live example returns data: [...] under the response body.
• Keep the scope read-only: this should not touch wallet key handling, transaction signing, broadcast behavior, or live-chain mutation.
• If maintainers want transaction-list behavior retained, keep it on the existing unconfirmed-transactions method rather than overloading getAddressUTXO().

Main acceptance criterion: UTXO callers should deterministically hit /address/utxo/{address} and receive UTXO records, while unconfirmed transaction-list callers continue to use their separate endpoint.