fix: Estimate relay transactions separately and combine with original transaction gas at quote time

[dan437]

Explanation

References

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 fee/gas computation for post-quote Relay flows, which can impact quoted costs and batching behavior; scope is localized but touches transaction-cost accuracy across multiple edge cases.

Overview
Post-quote Relay quoting now estimates gas for Relay deposit transactions only, then adds the caller-provided original transaction gas into the returned totals at quote time (including updated metamask.gasLimits, sourceNetwork estimate/max, and gas-fee-token amount calculations).

The combination logic prefers nestedTransactions[].gas over txParams.gas, handles EIP-7702’s single combined batch limit by adding original gas into that single value, and removes the previous toRelayParams path that mixed the original tx into gas estimation. Tests and the changelog are updated to cover these post-quote scenarios and edge cases (missing gas, fallback estimates, EIP-7702).

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