feat: persist pay strategy in TransactionController metamaskPay metadata

[OGPoyraz]

Explanation

TransactionPayController.transactionData (including quotes and their strategy) is not persisted, but transactionMeta.metamaskPay is. When a MetaMask Pay transaction finalizes after the transaction data is gone (e.g. the app restarted mid-flight), clients cannot report which pay strategy funded the transaction — mobile currently has to assume relay for all non-fiat backfills in its metrics builder (see MetaMask/metamask-mobile#34111).

This PR persists the strategy at the same point the rest of the pay metadata is synced:

• @metamask/transaction-controller: adds an optional strategy?: string field to MetamaskPayMetadata.
• @metamask/transaction-pay-controller: syncTransaction (called from updateQuotes) now writes the first executable quote's strategy to tx.metamaskPay.strategy. No-op quotes are already filtered out, so a direct route persists no strategy (consistent with mm_pay_strategy metrics semantics, which only count real quotes).

Non-breaking: the field is optional and additive.

References

• Consumer follow-up for refactor: cp-8.6.0 split getMetaMaskPayProperties into focused property helpers metamask-mobile#34111 (replaces the temporary relay assumption in the mm_pay_strategy metrics backfill once adopted)

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

Low Risk
Additive optional metadata and quote-sync wiring only; no auth, signing, or transaction lifecycle changes.

Overview
Adds an optional strategy field on persisted metamaskPay metadata so clients can tell which MetaMask Pay funding route was used after in-memory pay quote data is gone (e.g. after restart).

@metamask/transaction-controller extends MetamaskPayMetadata with strategy?: string. @metamask/transaction-pay-controller passes the first executable quote’s strategy from updateQuotes into syncTransaction, which writes it alongside existing fiat totals when pay metadata is synced. Direct / no-op routes (TransactionPayStrategy.None) still count as no executable quotes, so strategy stays unset, matching existing pay-metrics semantics. Tests cover successful persistence and the no-quote case.

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