fix(transaction-pay-controller): proxy Across status polling via configured api base

[pedronfigueiredo]

Summary

• route Across status polling through the configured Across apiBase instead of the direct upstream URL
• poll Across deposit status with depositTxnRef and accept fillTxnRef as a terminal transaction hash fallback
• read confirmations_pay from remote feature flags or local overrides, and use http://localhost:3000/across when confirmations_pay.dev is enabled without an explicit Across base
• add focused tests and changelog coverage for the new behavior

Validation

• yarn workspace @metamask/transaction-pay-controller run jest --no-coverage src/strategy/across/across-submit.test.ts src/utils/feature-flags.test.ts
• yarn eslint packages/transaction-pay-controller/src/strategy/across/across-submit.ts packages/transaction-pay-controller/src/strategy/across/across-submit.test.ts packages/transaction-pay-controller/src/utils/feature-flags.ts packages/transaction-pay-controller/src/utils/feature-flags.test.ts
• yarn workspace @metamask/transaction-pay-controller run changelog:validate
• yarn build

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Note

Medium Risk
Changes affect Across bridging completion detection and the returned terminal transaction hash, which could impact user-facing transaction tracking if the new status fields/URL behavior differs across environments.

Overview
Across submission now polls the Across deposit status endpoint via the configured config.across.apiBase and switches polling to use depositTxnRef (source tx hash) instead of depositId/chain params.

Status handling is expanded to treat fillTxnRef as an additional terminal transaction-hash fallback when destinationTxHash is missing, and tests/changelog are updated to cover the new polling URL and response fields.

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