fix: implement comprehensive security and governance improvements

[afurious]

This commit addresses multiple critical issues in the predictIQ protocol:

closes #192 Unchecked i128 Payout Multiplications

• Add ArithmeticOverflow error code for safe math operations
• Replace unsafe multiplication/division in claim_winnings with checked_mul/checked_div
• Add checked_add for total_staked and outcome_stake to prevent overflow
• Fix overflow in cancellation refund calculations
• Ensure high-inflation scenarios cannot cause accounting failures

closes #181 Missing resolved_at Update in resolution.rs

• Verify resolved_at timestamps are properly set in all resolution finalization paths
• Confirmed timestamps are correctly updated in finalize_resolution and admin_fallback_resolution
• Maintains temporal metadata integrity for market lifecycle tracking

closes #170 Hardcoded Resolution Constants in resolution.rs

• Add ConfigKey::VotingPeriod and ConfigKey::MajorityThreshold for governance control
• Implement get/set functions for voting period and majority threshold with safety bounds
• Replace hardcoded VOTING_PERIOD_SECONDS and MAJORITY_THRESHOLD_BPS with configurable values
• Add InvalidThreshold error code for parameter validation
• Enable protocol adaptation without contract upgrades

closes #191 Stubbed Referral Logic in place_bet

• Verify referral system is fully implemented with 10% fee allocation to referrers
• Confirm add_referral_reward properly calculates and stores referral rewards
• Verify claim_referral_rewards allows referrers to withdraw their earnings
• Ensure cancellation properly reverses referral rewards for market consistency

Security & Operational Improvements

• Enhanced arithmetic safety throughout financial calculations
• Improved governance flexibility with configurable resolution parameters
• Maintained backward compatibility while adding new configuration options
• Added proper error handling and validation for all new features

Files modified:

• src/errors.rs: Added ArithmeticOverflow and InvalidThreshold error codes
• src/types.rs: Added new ConfigKey entries for governance configuration
• src/modules/bets.rs: Implemented checked arithmetic for payout calculations
• src/modules/cancellation.rs: Added overflow protection for refund calculations
• src/modules/resolution.rs: Added configurable resolution parameters and getter/setter functions

All changes maintain the protocol's security guarantees while enhancing flexibility for different usage patterns and governance needs.

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