Add Oracle Mining Support (Optional Grading)

Summary

Implement optional two-stage selection for oracle/data mining applications with quality grading.

Background

Following PegNet's model, some applications need to grade data quality in addition to proof-of-work, particularly for oracle price feeds.

Requirements

Two-stage selection (PoW + grading)
Delta^4 scoring algorithm
Consensus value calculation
Iterative refinement process
Optional activation per mining account

Implementation Details

type OracleMiningData struct {
    LxrMiningSignature
    OracleData  map[string]uint64
    DataHash    [32]byte
}

func GradeOracleSubmissions(submissions []*OracleMiningData) []Winner {
    // 1. Filter top 50 by PoW
    // 2. Calculate consensus values (median)
    // 3. Grade using delta^4 scoring
    // 4. Iteratively remove worst grades
    // 5. Return final 10-25 winners
}

Acceptance Criteria

Oracle data structure support
Two-phase validation logic
Delta^4 scoring implementation
Median consensus calculation
Iterative refinement algorithm
Optional per mining account
Unit tests for grading algorithm
Integration tests with oracle data

Dependencies

Depends on: #3670 (Validation and Priority Queue)

Epic: &37
Specification: 32-lxr-mining.md (Section 9)
Reference: PegNet oracle mining