Prevent Li.Fi token request failures from unsupported chains

[ffaerber]

Summary

This change prevents the Li.Fi /tokens API request from failing when the application's chain list includes chains that Li.Fi doesn't support. Li.Fi rejects the entire request with a 400 error if any unsupported chain ID is included, so we now validate against supported chains first.

Key Changes

• Added fetchSupportedChainIds() function that queries the Li.Fi /chains endpoint to get the list of supported EVM chains
• Modified loadTokens() to filter CHAIN_IDS against the supported chains before making the /tokens request
• Added early return with empty object if no supported chains remain after filtering
• Added explanatory comment documenting the Li.Fi API behavior and the rationale for this approach

Implementation Details

• The supported chains are fetched from Li.Fi's /chains?chainTypes=EVM endpoint
• We intersect our internal chain list with Li.Fi's supported chains to ensure future unsupported chains (e.g., new networks added to our list) don't break token loading
• If all chains are filtered out, the function returns an empty cache object rather than making a request that would fail

https://claude.ai/code/session_01BhqRYS2cRAidqcFFxU84Nd