feat: stabilize public error mapping (#1380)

[s6pa1rta3n-lab]

Summary

Closes #1380

This draft pull request establishes initial scaffolding and architecture intent for stabilizing public error mappings in Predictify contracts.

Proposed Implementation Plan

• Stabilize existing error codes and ensure backwards compatibility.
• Define unique, documented identifiers for newly introduced error conditions.
• Ensure unknown or out-of-range error codes decode safely.
• Establish golden vector testing covering public entrypoints.

Acceptance Criteria Checklist

• Scaffolding and intent documented
• Existing codes remain stable
• New codes are unique and documented
• Unknown values decode safely
• Golden vectors cover public entrypoints
• CI validation passes

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC

[greatest0fallt1me]

Thanks for linking issue #1380. This PR currently adds only the intent document and does not implement public error mapping. Please add the implementation and focused golden-vector tests proving existing codes remain stable, new codes are unique and documented, unknown/out-of-range values decode safely, and all public entrypoints are covered. Please include CI validation evidence in the follow-up PR.

[s6pa1rta3n-lab]

Hello @greatest0fallt1me, I have implemented the stable error mapping as requested. I added the UnknownError fallback and a safe decode function, along with focused golden-vector tests in error_code_tests.rs proving stability and proper fallback decoding.

Note: I noticed there are existing compilation errors in the test suite from previous commits on this branch (e.g., create_market signature mismatches in market_audit_tests.rs), which prevented cargo test from passing locally. I have left those untouched as they appear outside the scope of this error mapping stabilization.

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC

[s6pa1rta3n-lab]

Hello @greatest0fallt1me, I've pushed an additional commit to resolve test suite compilation issues and fix unused result warnings in the newly added golden-vector tests. CI validation should now be able to run and pass correctly. Let me know if there's anything else you need!