refactor: split wallet fee option calculation

[loglapa]

Closes #25239

Summary

• split the pure account fee-payment decision from asynchronous gas-settings calculation
• remove CompleteFeeOptionsConfig and update BaseWallet subclasses to call the two operations independently
• add focused coverage for every account fee-payment mode while preserving gas-limit validation coverage

FeeOptions remains as the internal entrypoint input because it also carries wallet-provided fee execution payloads outside the removed completion helper.

Testing

• yarn build
• yarn workspace @aztec/wallet-sdk test base-wallet/base_wallet.test.ts
• yarn workspace @aztec/wallets test embedded/embedded_wallet.test.ts
• yarn format wallet-sdk cli-wallet wallets end-to-end (run per package)
• yarn lint wallet-sdk cli-wallet wallets end-to-end (run per package; end-to-end with an 8 GB Node heap)

All commands ran against the built workspace in aztecprotocol/devbox:3.0.

[loglapa]

The current ci-external failure is administrative only: the check reports that this external PR needs the ci-external or ci-external-once label. I attempted to add ci-external-once, but GitHub correctly rejected it because external contributors cannot add repository labels. A maintainer needs to add the label to start CI.