feat: add event fee treasury variant

[JTKaduma]

PR Description

Summary

This PR adds global event-fee treasury tracking for ticket purchases while preserving the existing per-pool fee split.

When a ticket is bought, the contract now continues to:

• credit the event creator's pool share
• credit the pool-specific platform fee bucket

and also:

• accumulate the fee portion into EventFeeTreasury for centralized event-fee withdrawals/reporting

What Changed

• Added StorageKey::EventFeeTreasury usage in buy_ticket to track aggregate event fees across ticket purchases.
• Simplified TicketType default handling by deriving Default and marking Standard as the default variant.
• Updated pool_created event plumbing to pass a single details tuple payload instead of multiple discrete parameters.
• Scoped second_crowdfunding test-only interfaces behind #[cfg(test)] so they do not leak into non-test builds.
• Added/expanded ticket-purchase tests to verify:
  • zero-fee purchases fully credit the event pool
  • per-pool fee buckets accumulate correctly
  • the global EventFeeTreasury is updated correctly across purchases

Why

This gives the contract a dedicated aggregate treasury for event fees, which makes fee accounting and withdrawals more straightforward without removing the existing per-pool revenue tracking.

Testing

• Ran cargo test -q
• Result: 230 passed; 0 failed

Closes #182

[Akshola00]

@JTKaduma ci is failing