refactor(assets-controller): memoize balance call encodings in Multic…

[salimtb]

…allClient

Cache encodeBalanceOf and encodeGetEthBalance per account address to avoid redundant ABI encoding when batching many tokens for the same wallet.

Explanation

References

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

Low Risk
Internal performance refactor with no API or balance semantics change; risk is limited to ensuring cached calldata stays identical to prior per-request encoding.

Overview
MulticallClient.batchBalanceOf now builds ERC-20 balanceOf and native getEthBalance calldata once per account (case-insensitive) per invocation, instead of re-encoding for every token row in a batch.

A per-request createBalanceCallDataCache backs multicall aggregate3 assembly via buildAggregate3BalanceCalls, and the same cache is passed through multicall fallback and unsupported-chain single-call paths so ERC-20 fallback reuses encoded calldata. Native balances on those fallback paths still use provider.getBalance (unchanged).

A unit test asserts encoding deduplication (e.g. two balanceOf and one getEthBalance encode for four mixed requests). Changelog updated under Unreleased.

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