chore: imporove `swap_rate_v3` rpc

[syan095]

Pull Request

Closes: PRO-1830 Closes: PRO-1370

Checklist

Please conduct a thorough self-review before opening the PR.

• [x] I am confident that the code works.
• [x] I have written sufficient tests.
• [x] I have written and tested required migrations.
• [x] I have updated documentation where appropriate.

Summary

Improved the swap_rate_v3 RPC call and runtime API cf_pool_simulate_swap

• Added boost_fee (taken first before all other fees)
• Added swap_input (input - ingress_fee - boost_fee)
• Intermediary returns None/Null if output == stable asset

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 15.78947% with 16 lines in your changes missing coverage. Please review.

Project coverage is 72%. Comparing base (8e1619a) to head (ebe1e0a). Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
state-chain/custom-rpc/src/lib.rs	20%	8 Missing :warning:
state-chain/runtime/src/lib.rs	0%	0 Missing and 8 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5430 +/- ## ====================================== - Coverage 72% 72% -0% ====================================== Files 490 490 Lines 86892 86786 -106 Branches 86892 86786 -106 ====================================== - Hits 62395 62218 -177 - Misses 21563 21626 +63 - Partials 2934 2942 +8 ```

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[syan095]

I don't think this addresses PRO-1370 as the issue is intended.

Ah, I missed all the conversation in that linear ticket - it was added as a last-minute thing and I should not have been so presumptuous. I will hold off on this until we can get spec locked down.

[dandanlen]

I'll close this for now, we can come back to it when we have some agreement.