fix: cp-7.58.0 percentage buttons in perps deposit

[matthewwalsh0]

Description

Fix percentage buttons in Perps deposit, by converting balance to USD if required.

Partial cherry-pick of #21529 for 7.58.0.

Changelog

CHANGELOG entry: null

Related issues

Fixes: #21751

Manual testing steps

Screenshots/Recordings

Before

After

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.

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.

---

Note

Percentage buttons now compute amounts from fiat-converted balance (handles USD override for perps deposits) with supporting tests.

• Hooks:
  • useTransactionCustomAmount: use useTransactionPayFiat.convertFiat to derive payTokenBalance in useTokenBalance, ensuring percentage calculations use the selected fiat (e.g., USD override for perps deposits).
• Tests:
  • useTransactionCustomAmount.test.ts: add CurrencyRateController mock data and a test verifying percentage calculation converts to USD for TransactionType.perpsDeposit.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
75.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Cal-L]

LGTM