Description

This change migrates Card feature hooks from the legacy BN.js / app/util/number helpers to the native BigInt module at app/util/number/bigint, following the repository bigint migration guide.

Reason: Reduce BN.js usage, align Card code with the bigint utilities, and keep behavior equivalent for balances, delegation amounts, and gas-faucet checks.

What changed:

• useAssetBalances.tsx — import balanceToFiatNumber from util/number/bigint; test mock updated to match.
• useCardDelegation.ts — import toTokenMinimalUnit from util/number/bigint; tests mock bigint return values instead of decimal strings.
• useNeedsGasFaucet.ts — remove bnjs4; use hexToBigInt for wei gas price and balance; compare with native <; multiply with BigInt(gasLimitWithBuffer); cast decGWEIToHexWEI result to string for TypeScript (legacy conversionUtil union type).

Changelog

CHANGELOG entry: null

Related issues

No issue: internal refactor (Card BigInt burndown / migration guide).

Manual testing steps

Feature: Card hooks BigInt migration

  Scenario: Unit tests cover migrated hooks
    Given the branch is checked out with dependencies installed
    When the developer runs `yarn jest app/components/UI/Card/hooks/useAssetBalances.test.ts app/components/UI/Card/hooks/useCardDelegation.test.ts app/components/UI/Card/hooks/useNeedsGasFaucet.test.ts`
    Then all tests pass

  Scenario: Optional smoke on Card delegation flow
    Given a dev build on a test network with Card funding available
    When the user opens Card home and triggers a flow that uses delegation or gas faucet logic
    Then balances and gas-faucet behavior match expectations (no regression vs prior build)

Screenshots/Recordings

Before

N/A

After

N/A

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Mobile Coding Standards.
• I've completed the PR template to the best of my ability
• I've included tests if applicable
• I've documented my code using JSDoc format if applicable
• I've applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Performance checks (if applicable)

• I've tested on Android
  • Ideally on a mid-range device; emulator is acceptable
• I've tested with a power user scenario
  • Use these power-user SRPs to import wallets with many accounts and tokens
• I've instrumented key operations with Sentry traces for production performance metrics
  • See trace() for usage and addToken for an example

For performance guidelines and tooling, see the Performance Guide.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.