fix(transaction-controller): harden gas fee token preflight

[jpuri]

Explanation

Predict claim on Mobile (Polygon Safe wallets) can fail during gas-station preflight when a gas fee token (e.g. pUSD) is pre-selected but Sentinel returns an empty gasFeeTokens list and native POL is insufficient.

Two controller bugs contribute to confusing failures and bad publish fallbacks:

1. isNativeBalanceSufficientForGas treated missing maxFeePerGas/gasPrice as zero, so gas × 0 = 0 made every wallet look able to pay native gas. That could clear selectedGasFeeToken while gas estimates were still in flight (common with skipInitialGasEstimate), leading to publishes with intrinsic gas too low: gas 0.
2. checkGasFeeTokenBeforePublish set isExternalSign: true and cleared nonce before validating the selected token. When validation failed (Gas fee token not found and insufficient native balance), transaction metadata could remain in external-sign mode even though signing was never completed.

This PR hardens both paths:

• balance.ts: return insufficient when gas or fee fields are unset, so pre-selected gas fee tokens are not cleared prematurely.
• gas-fee-tokens.ts: only enable external sign after the selected token is confirmed in freshly fetched gasFeeTokens; on failure, persist refreshed tokens but reset isExternalSign to false before throwing.

No breaking API changes. Scope is limited to @metamask/transaction-controller publish-time gas-fee-token gating.

References

https://consensyssoftware.atlassian.net/browse/CONF-1725

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 publish-path balance and gas-fee-token validation; incorrect behavior could block valid publishes or alter signing mode, but scope is limited to preflight gating with targeted tests.

Overview
Hardens publish-time gas fee token gating in @metamask/transaction-controller so pre-selected tokens are not dropped and external-sign state is not left inconsistent when preflight fails.

isNativeBalanceSufficientForGas now returns insufficient when gas or fee fields (maxFeePerGas / gasPrice) are unset, instead of treating missing values as zero. That stops in-flight gas estimates (e.g. with skipInitialGasEstimate) from looking like free native gas and clearing a selected gas fee token too early.

checkGasFeeTokenBeforePublish only sets isExternalSign: true and clears nonce after confirming the selected token appears in freshly fetched gasFeeTokens. If the token is missing, it persists the refreshed token list, resets isExternalSign to false, then throws—avoiding metadata stuck in external-sign mode after a failed preflight.

Tests and an Unreleased changelog entry cover the new behavior.

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