fix: weth incorrectly resolves to eth info

[NikolasHaimerl]

Fix WETH/ETH Symbol Resolution

Linear: ACX-4369

📝 Summary

This pull request addresses a bug where the swap/approval endpoint was incorrectly resolving the symbol for wrapped native tokens (like WETH) as the native token symbol (e.g., ETH). This was happening on chains like Base and Linea where the wrapped native token address is also present in the TOKEN_SYMBOLS_MAP under the ETH symbol.

🔧 Changes

• Modified the getTokenByAddress function in api/_utils.ts to correctly resolve the token symbol in cases of ambiguity between ETH and WETH.
• Added a comprehensive test suite for getTokenByAddress to ensure the correct symbol is returned for all supported chains.

💭 Rationale

The root cause of this issue lies in the @across-protocol/constants package, where some wrapped native token addresses are associated with both ETH and WETH symbols. The getTokenByAddress function was not deterministically picking the correct symbol, sometimes defaulting to ETH when it should have been WETH.

This pull request implements a solution that prioritizes WETH when a token address is associated with both symbols. This is a robust solution because it correctly handles the ambiguity in the constants file and ensures that the correct token symbol is used throughout the application.

The alternative of fixing the constants file is not feasible as it is an external dependency. This solution provides a local fix that is both effective and maintainable.

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[NikolasHaimerl]

Closing in favour of #1867