Global dispute analytics and transparency log 206

[Stanley-Owoh]

Summary
Implemented Global Dispute Analytics and Transparency Log (Theme: Part 11: Dispute Resolution V2) and fixed critical fund release logic issues.
Changes Made

1. Global Dispute Analytics (types.rs)

• Added new DataKey entries: TotalReleasedCount, TotalRefundedCount, TotalCancelledCount
• Added GlobalDisputeAnalytics struct with fields for tracking escrow outcomes and failure rates

2. Analytics Functions (lib.rs)

• Added analytics_summary() - returns global dispute analytics including failure rate in basis points
• Added getter functions: get_total_released_count(), get_total_refunded_count(), get_total_disputed_count(), get_total_cancelled_count()

3. Fund Release Logic Fixes

• Critical Fix: verify_delivery was NOT updating TotalReleasedAmount - now correctly tracks cumulative released amounts
• Critical Fix: execute_mediation_settlement was using seller_amount (before fees) instead of net_seller (after fees) - fixed to prevent overcounting
• Added TotalRefundedCount increment to mediation settlement path
• Added FundsReleasedEvent to execute_mediation_settlement for event consistency
  Verification Checklist
• TotalReleasedAmount updated cumulatively, not overwritten
• Partial releases correctly increment the released total
• No double-counting across multiple release paths
• Released amounts use net amounts (after fees deducted)
• State updates and events reflect correct totals

Closes #206