feat: add decentralized oracle aggregator with medianizer and outlier trimming (#69)

[bellofuad34-ctrl]

Closes #69

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Summary

Implements a decentralized oracle aggregator with medianizer and outlier trimming, addressing #69.

Changes

• contracts/oracle-aggregator/src/lib.rs: New Soroban contract OracleAggregator that:
  • Accepts price pushes from N authorized data feeds (add_feed / remove_feed, admin-only).
  • Computes a manipulation-resistant median price, not a mean, so a single spiked feed cannot skew the result.
  • Performs iterative outlier trimming: values whose deviation from the running median exceeds a configurable threshold (in basis points, default 5%) are dropped before the final median is computed.
  • Enforces heartbeat staleness: price updates older than a configurable window (default 300s) are rejected at write time and ignored at read time.
  • Uses strict fixed-point integer math (u128 with saturating_mul, no floating point, no overflow risk).
  • Requires auth on admin operations and feed pushes.
• contracts/oracle-aggregator/src/math.rs: Pure, overflow-safe math module (median, median_of_sorted, trimmed_median, deviation_bps, is_outlier, is_stale, mid) with exhaustive unit tests.
• contracts/oracle-aggregator/tests/oracle_aggregator_tests.rs: Property-based tests (proptest) verifying mathematical safety across edge-case input vectors (extreme u128 values, zero references, clustered adversarial feeds), plus end-to-end contract tests including the required +500% spike scenario (1 of 5 oracles spiked; aggregated price stays stable).
• Cargo.toml: Registers the contract as a workspace member and removes lto/panic from the per-package profile override (these keys are invalid in [profile.*.package.*] per the Cargo reference and blocked the whole workspace from parsing; CI on main was already red on Build).
• Cargo.lock: Updated for the new workspace member.

Verification

• cargo build -p oracle-aggregator --target wasm32-unknown-unknown --release succeeds.
• cargo test -p oracle-aggregator passes: 8 unit tests + 12 integration/property tests.
• cargo clippy -p oracle-aggregator is clean.
• End-to-end: with 4 honest feeds at ~100 and 1 feed at +500%, get_price returns the honest median (100), not the spike.

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[agnesnaomiolim-cloud]

This branch has a conflict; resolve it.

[agnesnaomiolim-cloud]

CI check failed; please resolve that.

[bellofuad34-ctrl]

Hi maintainers 👋 -- this PR is ready for review and merge.

What has been updated:

• Merge conflict resolved: latest main merged into feat/69-oracle-aggregator; Cargo.lock/Cargo.toml conflicts fixed (contracts/oracle-aggregator retained as a workspace member). PR is now mergeable.
• security-scan workflow fixed: the compliance-kube-bench job referenced ${{ matrix.os }} with no matrix defined, which invalidated the whole workflow and made every run fail before starting a job. Corrected the kube-bench download URL, fixed escaping, and pointed the k6 job at the existing grafana/k6-action and benchmarks/k6/security-pen.js.

Maintainer actions needed:

1. Approve the pending workflow runs -- several checks (CI/CD Pipeline, Lint, etc.) are waiting on first-time-contributor approval.
2. Note: the security-scan check still shows red on this PR because GitHub runs the base branch's workflow file for fork PRs; the broken file lives on main. This PR includes the fix, so it will take effect on main after merge. (Main also has unrelated pre-existing issues -- an invalid kube feature leader-election and a corrupted src/controller/leader.rs -- that affect all PRs.)

Could you review and merge? Thanks!

[bellofuad34-ctrl]

@agnesnaomiolim-cloud this PR is ready to merge -- branch conflict is resolved and the broken security-scan workflow has been fixed in this branch. Could you please approve the pending workflow runs and merge? Thank you!