Oracle relies on a single data source with no fallback

[yusuftomilola]

contracts/contrib/oracle.rs appears to use a single oracle source with no fallback or median-of-multiple-sources design, so one bad feed could corrupt downstream state.

[VeronicDev]

@VeronicDev has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hello Maintainer, I can fix this please assign.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @VeronicDev to this issue.

[Ranjeet2063]

Hi team,

Happy to tackle this. Here is how I plan to implement it:

Technical outline:

1. Audit storage layout and state invariants ensuring strict auth guards.
2. Implement deterministic state transitions with safe checked arithmetic.
3. Add hermetic unit and regression tests covering authorized, unauthorized, and boundary edge cases.
4. Profile instruction and CPU/gas limits under Soroban host environment.

Let me know if this aligns with the repository guidelines and assign when convenient.