fix(fees): per-market fee provenance and ledger migration (closes #178) - #186

@abimbolaalabi The PR introduces per-market fee ledgers and derived totals, but it does not fully solve issue #178. Critical gaps: 1) The migration function migrate_fee_ledger is referenced but not defined in the diff; without it, existing deployments cannot migrate. 2) The migration only snapshots the global AccumulatedFees into LegacyFees, but does not migrate existing per-market fees (if any) from the old model. 3) cancel_market now reclaims the full per-market ledger balance, which reintroduces fee theft: a malicious creator can inflate their market's ledger (e.g., via direct storage manipulation) and drain fees that belong to other markets. The old code capped reclaim at pool-derived fees to prevent this; the new code removes that safeguard. 4) compute_total_proven_fees iterates over all markets, which could exceed gas limits with many markets. 5) Tests do not cover migration from existing per-market fees or the fee theft scenario. Please address these issues and add corresponding tests.

@abimbolaalabi This PR does not fully resolve issue #178. The global AccumulatedFees counter is still present and used as a cached total, which reintroduces the cross-market contamination risk. cancel_market now reclaims only pool-derived fees (capped), not the full per-market ledger balance, so it does not correctly reclaim all fees attributable to that market. The migration only snapshots the old global value into LegacyFees but does not clear the global counter or redistribute fees into per-market ledgers. To fix, you must: (1) remove the global AccumulatedFees counter entirely and derive totals from per-market ledgers (plus LegacyFees for pre-migration funds); (2) on cancel_market, reclaim the full per-market ledger balance for that market; (3) implement a migration that moves the legacy global balance into a per-market ledger (e.g., a special market ID) or at least ensures no cross-market contamination; (4) add tests that specifically verify cancelling one market does not affect another market's fees when both have fees; (5) run CI and provide evidence of passing tests. Please address these issues and resubmit.

@abimbolaalabi This PR attempts to fix #178 but has critical issues. The migration only snapshots the global AccumulatedFees into LegacyFees, losing per-market provenance for existing fees. The new compute_total_proven_fees iterates over all market IDs up to MarketCount, which is incorrect if markets are deleted or IDs are not contiguous. cancel_market now reclaims the full per-market ledger balance, but this balance may include fees from other markets if migration or accounting is flawed. debit_proven_fees drains LegacyFees first, which may not be attributable to any market, allowing cross-market fee theft. Also, get_market_ttl now returns 1 instead of the actual TTL, breaking the API contract. The removal of the config_changed event and leaderboard record_bet logic is unrelated and concerning. The referral registry changes are not visible in the diff, so correctness cannot be verified. Please address these issues and provide CI results before approval.