Implement Mining Validation and Priority Queue

Summary

Implement the core validation logic and priority queue management for mining submissions.

Background

Mining submissions need to be validated against baseline difficulty and ranked in a priority queue to determine winners.

Requirements

Validate proof-of-work meets baseline difficulty
Implement priority queue for top-N tracking
Handle competitive threshold comparisons
Verify miner registration in keybook

Implementation Details

func ValidateLxrMiningSignature(sig *LxrMiningSignature, miningAccount *MiningAccount) error {
    // 1. Check miner is registered
    // 2. Verify proof-of-work
    // 3. Check baseline difficulty
    // 4. Update priority queue if competitive
}

type PriorityQueue struct {
    entries []MiningEntry
    maxSize int
}

Acceptance Criteria

PoW validation with LXRHash
Baseline difficulty checking
Priority queue with proper ordering
Competitive threshold logic
Miner registration verification
Unit tests for validation logic
Performance tests for queue operations

Dependencies

Depends on: #3669 (Mining Account Type)

Epic: &37
Specification: 32-lxr-mining.md