Add per-market oracle-deviation history with rolling median outlier detection

[greatest0fallt1me]

Description

Per-market oracle deviation is currently a single bound. Track a rolling deviation history and reject quotes that deviate from the rolling median by more than a configurable z-multiple.

Requirements and Context

• Add OracleDeviationHistory storage per market_id (ring buffer)
• Compute rolling median in oracles.rs::OracleUtils
• Reject with Error::OracleQuoteOutlier
• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b feat/oracle-rolling-deviation

2. Implement changes
   • contracts/predictify-hybrid/src/oracles.rs
   • contracts/predictify-hybrid/src/storage.rs
3. Test and commit
   • cargo test -p predictify-hybrid oracle -- --nocapture
   • Cover edge cases: empty history, all-same history, large deviation
   • Include test output and notes in the PR

Example commit message

feat: rolling-median deviation outlier rejection

Acceptance Criteria

• Outlier rejection deterministic
• History size from config
• No unwrap() introduced
• Documented in oracles.rs

Guidelines

• Avoid floating point; use i128 math
• Minimum 95% coverage
• Clear documentation and inline comments
• Timeframe: 96 hours

[fadesany]

@fadesany has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello maintainer, i would like to work on this issue

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Congratulations, @fadesany! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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[grantfox-oss]

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #631)
2. Your PR will be reviewed by the Predictify-org maintainers

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