Buy orders with same sell buy token

[ashleychandy]

Description

Enable sell=buy handling for native-equivalent trades by treating native wrapped token to ETH marker as same-token during order validation.
This is needed because the conversion path already exists downstream, but validation previously rejected these orders early.

Changes

• Updated same-token validation logic to consider native wrapped token sell + ETH marker buy as same-token for policy evaluation.
• Preserved existing policy behavior: allow-sell permits Sell orders, while Buy orders remain rejected.
• Added unit test coverage for native-equivalent same-token cases under both disallow and allow-sell behavior.
• Added e2e coverage for:
• native-equivalent Sell quote/order success
• native-equivalent Buy quote rejection under allow-sell policy

How to test

1. cargo nextest run -p shared pre_validate_err pre_validate_same_tokens_allow_sell
2. cargo nextest run -p e2e local_node_native_same_token_sell_with_eth_buy_marker local_node_native_same_token_buy_with_eth_buy_marker_rejected --test-threads 1 --run-ignored ignored-only --failure-output final

Related Issues

Fixes #4053

[gemini-code-assist]

Code Review

No critical issues found.

[github-actions]

This pull request has been marked as stale because it has been inactive a while. Please update this pull request or it will be automatically closed.

[m-sz]

Hello @ashleychandy, thank You for Your contribution. I will review it thoroughly and we will either work together to ensure a smooth review or I might take over it to incorporate into a PR I am already working on. Will reach back to You tomorrow.

[ashleychandy]

Hey @m-sz,
Thanks for taking a look, I appreciate it.

I’ve just pushed a small refactor to the validate_same_sell_and_buy_token logic along with some additional test coverage to make the behavior clearer and easier to reason about.

Happy to iterate based on your feedback, or if it fits better with your ongoing PR, I’m also fine with you incorporating the changes there. Just let me know how you’d prefer to proceed.