Account balance zeroing

[Prithpal-Sooriya]

Explanation

• What is the current state of things and why does it need to change?
  The AccountsApiBalanceFetcher was incorrectly zeroing out ERC-20 token balances for accounts that were not part of the current balance fetch request. This could lead to incorrect balance displays, particularly when fetching balances for a single selected account while other accounts had existing (but not requested) balances.

• What is the solution your changes offer and how does it work?
  This PR introduces a new condition, isAccountIncludedInRequest, to the shouldZeroOutBalance logic. This ensures that ERC-20 balances are only zeroed out if the account being processed is explicitly part of the current balance fetch request (either the selectedAccount or one of the allAccounts if queryAllAccounts is true).

• Are there any changes whose purpose might not obvious to those unfamiliar with the domain?
  The addition of isAccountIncludedInRequest and its integration into the shouldZeroOutBalance condition is crucial to prevent unintended zeroing of balances for accounts not in the scope of the current query.

References

• Fixes [Bug]: Fiat balance not displayed for accounts with asset balance in accounts list dropdown, possibly related to accounts with only mUSD balance metamask-mobile#26707
• Fixes https://consensyssoftware.atlassian.net/browse/ASSETS-2814

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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