fix: deduplicate ERC20 batch approvals

[Mabolla]

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Summary

Deduplicates ERC20 approvals in batchApproveAssets when the same token contract appears multiple times, including addresses that differ only by casing.

Root cause

batchApproveAssets already tracks processed contract addresses for NFT approvals, but the ERC20 branch did not use that set. Duplicate entries could therefore generate multiple identical approve(conduit, MAX_UINT256) calls and unnecessarily take the multicall path.

Changes

• Normalize ERC20 contract addresses to lowercase before deduplication.
• Reuse processedContracts so only one unlimited approval is generated per ERC20 contract.
• Add a deterministic regression test covering duplicate ERC20 entries with different address casing.

Validation

• Regression test reproduced the duplicate-approval behavior before the fix and passes after it.
• Targeted tests: 11/11 passed.
• Full unit suite: 928/928 passed across 41 test files.
• Biome check passes for the two changed files.