feat: Derive fiat order sourceAmount from on-chain tx data and persist fiat order metadata

[OGPoyraz]

Explanation

1. Derive fiat order sourceAmount from on-chain tx data

Currently, the fiat submit flow derives sourceAmountRaw from order.cryptoAmount - a human-readable value reported by the on-ramp provider. This value may not precisely reflect what was actually received on-chain.

This PR reads the actual transferred amount from the completed on-chain transaction (order.txHash) instead. For native tokens, the amount is taken from tx.value. For ERC-20 tokens, the amount is decoded from the transfer(address,uint256) call data. If the on-chain read fails or the transaction hash is missing, the existing order.cryptoAmount derivation is used as a fallback.

The implementation introduces:

• getTransferredAmountFromTxHash - a generic utility in utils/transaction-receipt.ts that reads transferred amounts from any on-chain transaction (native or ERC-20). Takes explicit chainId and tokenAddress params for reusability.
• resolveSourceAmountRaw - a fiat-strategy-specific function in strategy/fiat/utils.ts that orchestrates the on-chain read with order.cryptoAmount fallback.
• getRawSourceAmountFromOrderCryptoAmount - the existing decimal-shift conversion, moved from fiat-submit.ts to strategy/fiat/utils.ts and renamed for clarity.

2. Persist fiat order metadata on metamaskPay

The TransactionPayController state is cleaned up when a transaction is finalized (confirmed/failed/dropped). This means fiatPayment.orderId and the provider info are gone by the time the user opens the activity/transaction-details view.

To enable the mobile activity view to show a fiat order status row (and query RampsController:getOrder for live status), this PR persists the fiat order ID and provider code on transaction.metamaskPay before polling begins in submitFiatQuotes.

Changes:

• MetamaskPayMetadata (transaction-controller/types.ts) — Added fiatOrderId?: string and fiatProvider?: string fields.
• submitFiatQuotes (fiat-submit.ts) — Calls updateTransaction to persist fiatOrderId and fiatProvider on tx.metamaskPay before waitForOrderCompletion starts polling. This ensures data is available even while the order is still in-flight.
• Tests — Two new tests verify metadata persistence and that existing metamaskPay fields are preserved.

References

• Related to the fiat strategy submit flow introduced in feat: Implement FiatStrategy submit flow with order polling and relay execution #8347

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Medium Risk
Touches the fiat submission path by introducing on-chain transaction reads and persisting new metadata onto transactions; failures or unexpected tx shapes could affect quote amounts or activity display, though fallbacks and tests mitigate this.

Overview
Improves MetaMask Pay fiat submissions by deriving the relay sourceAmountRaw from the completed on-chain transaction (order.txHash) when possible (native tx.value or decoded ERC-20 transfer calldata), falling back to order.cryptoAmount if the read fails or is unavailable.

Persists fiat on-ramp order identifiers onto the transaction (transaction.metamaskPay.fiatOrderId / fiatProvider) before order polling begins so downstream activity views can query order status even after controller state cleanup. Adds a reusable getTransferredAmountFromTxHash utility plus new/updated unit tests and changelog entries.

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