fix: fall back to zero-address for native tokens without slip44

[n3ps]

Explanation

EVM native tokens without a slip44 mapping (e.g. Chiliz) left assetId undefined.

Fall back to the zero-address ERC-20 CAIP-19 form (eip155:<chainId>/erc20:0x000…000) so clients can resolve based still based on assetId by deriving the chain id.

References

N/A

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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