Analytics and metrics module

[nafiuishaaq]

Description:
Add on-chain view functions for contract analytics.

Acceptance Criteria:

total_volume_locked() -> i128 — sum of all locked amounts.

total_fees_collected() -> i128 — total fees sent to treasury.

active_sessions_count() -> u32 — sessions in Locked or Completed state.

dispute_rate() -> (u32, u32) — disputes vs total sessions.

average_resolution_time() -> u64 — average ledgers to resolve dispute.

Labels: integration, analytics, view-functions