feat(transaction-pay-controller): expose required transaction count

[dan437]

Explanation

Expose the expected number of TransactionController child transactions on Relay-backed payment quotes. The value uses the same Relay submission logic, handles EIP-7702 batches as one transaction, and stays undefined for unsupported paths.

This belongs in the controller because only it knows whether Relay steps will become one EIP-7702 batch or multiple sequential TransactionController transactions. Keeping that logic in Core prevents clients from parsing provider-specific quote data and duplicating submission rules.

Relay quotes also avoid gas fee token sponsorship when the source account cannot use EIP-7702. Eligibility must be correct at the quote source so every client avoids unsupported hardware routes. The Mobile consumer depends on this PR and a package release before it can use requiredTransactionCount.

References

• Consumer: feat: dismiss Ledger prompt after deposit signing (CONF-1715) metamask-mobile#34872

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
Changes Relay quote fee presentation and adds a new quote field used by Mobile pay UX; incorrect counts or gas-station gating could mislead confirmation flows or offer unsupported EIP-7702 sponsorship.

Overview
Relay-backed TransactionPayQuote values can now include an optional requiredTransactionCount, computed during quote normalization so clients know how many TransactionController child transactions execution will create without re-parsing Relay steps.

The count reuses getRelayTransactionStepData (now exported and typed against raw RelayQuote): sequential flows report one per local step, EIP-7702 batches report 1, and the field is omitted when the count is unknown (execute quotes, post-quote / payment-override / HyperLiquid / Polymarket deposit paths, empty or malformed step data).

Gas fee token sponsorship on Relay quotes is gated on accountSupports7702: when the source account does not support EIP-7702, calculateSourceNetworkCost skips the gas station path so quotes no longer set fees.isSourceGasFeeToken or call gas-fee-token lookup—aligning quoted fees with hardware and other non-7702 accounts.

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[matthewwalsh0]

The pay controller is just one instance where we call addTransactionBatch and may sequentially sign if EIP-7702 is supported.

So rather than coupling the modal to every instance that does this, should we instead provide this information at the source within the TransactionController?

Maybe some transient state such as signatureCounts that is keyed on batch ID that is set within addTransactionBatch?

Then the hardware modal can check using the batchId of the transaction it's signing?