feat: implement batch claim winnings for multiple events in one transaction

[greatest0fallt1me]

Description:

Allow a user to claim winnings for multiple resolved events in a single transaction to save gas and improve UX.

Requirements and Context:

• Must be secure, tested, and documented
• Should add claim_winnings_batch(user, event_ids: Vec<Symbol>) (or equivalent)
• Should validate each event is resolved and user is winner; claim all or none (atomic)
• Should emit events per claim or batch
• Must enforce same rules as single claim_winnings (no double claim)
• Should be gas-efficient

Suggested Execution:

1. Fork the repo and create a branch

   git checkout -b feature/batch-claim-winnings

2. Implement changes

   • Write contract: src/lib.rs (add claim_winnings_batch)
   • Update storage and events; add documentation and NatSpec-style comments

3. Test and commit

   • Run tests; cover full success, partial failure (atomic revert), double claim
   • Include test output and security notes

Example Commit Message:

feat: implement batch claim winnings for multiple events in one transaction

Guidelines:

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 48 hours