feat: TokenBalanceController architect handling unprocessed tokens

[Prithpal-Sooriya]

Explanation

• What is the current state of things and why does it need to change?
  Previously, the AccountsApiBalanceFetcher would zero out balances for non-native tokens it couldn't retrieve. The TokenBalancesController would then only pass on unsupported chains to subsequent fetchers. This prevented the RPC balance fetcher from attempting to retrieve balances for these "missed" tokens. Additionally, TokenDetectionController had noisy console.warn logs for token metadata cache misses.

• What is the solution your changes offer and how does it work?
  This PR modifies the balance fetching flow to return "unprocessed tokens" for non-native tokens that the AccountsApiBalanceFetcher cannot process. These unprocessedTokens are then explicitly passed through the TokenBalancesController to subsequent fetchers. The RpcBalanceFetcher now accepts these unprocessedTokens and, when provided, will only fetch balances for those specific tokens, avoiding redundant work for native or staked tokens. The console.warn logs in TokenDetectionController have also been removed.

• Are there any changes whose purpose might not obvious to those unfamiliar with the domain?
  The introduction of the unprocessedTokens parameter and its propagation across fetchers is key. When unprocessedTokens are present, the RPC fetcher operates in a targeted mode, only querying for the specified ERC-20 tokens, rather than performing a full chain-wide balance fetch.

• If your primary goal was to update one package but you found you had to update another one along the way, why did you do so?
  The change required modifications across api-balance-fetcher, TokenBalancesController, and rpc-balance-fetcher to correctly implement the "unprocessed tokens" handoff and fallback mechanism. TokenDetectionController was updated to remove noisy logs as requested.

Code Walkthrough:
https://www.loom.com/share/c38c5369dcb54d62908747078a899be9

• If you had to upgrade a dependency, why did you do so?
  No dependency upgrades were required.

References

• https://consensyssoftware.atlassian.net/browse/ASSETS-2871

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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