Task: Dispute tally property tests & resolved outcome summary cache

[Dopezapha]

Closes #553
Closes #547

Summary

Property tests for DisputeManager::calculate_dispute_outcome`

Files changed: property_based_tests.rs, tests/dispute_stake_tests.rs

Added a proptest suite and deterministic unit tests covering all required invariants for
DisputeUtils::calculate_stake_weighted_outcome and DisputeManager::calculate_dispute_outcome:

Test	Invariant
deterministic_tally	Same inputs always produce the same outcome
tie_resolves_to_reject	Equal support/against stake resolves to false (reject)
monotonic_in_support_stake	Adding more support stake never flips a winning outcome to losing
empty_stakes_no_panic	Zero-stake voting completes without panic
dispute_tally_single_voter_support	Single supporter with no opposition always wins
dispute_tally_all_equal_stakes_is_tie	Tie case confirmed to reject

All tests use real DisputeVoting / DisputeVote types from disputes.rs.
Edge cases covered: empty set, single voter, all-equal stakes, monotonic increase.

ResolvedOutcomeSummary cache in resolution.rs

Files changed: resolution.rs, lib.rs, bets.rs, disputes.rs

Precomputes and persists a ResolvedOutcomeSummary struct
(winning_total, total_pool, num_winning_outcomes) once at resolution time via
ResolutionOutcomeCache::refresh(), eliminating repeated full-bet-set iteration on every
payout/claim call.

Payout paths updated to O(1) cache reads:

• lib.rs::distribute_payouts → ResolutionOutcomeCache::require() (line 3300)
• lib.rs::claim_winnings → ResolutionOutcomeCache::require() (line 1881)

Cache invalidation:

• ResolutionOutcomeCache::invalidate() called before admin outcome override
• disputes.rs calls refresh() after dispute-driven outcome change
• require() includes a staleness guard: re-computes automatically if total_pool or
  num_winning_outcomes drifts from cached values

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