feat: add standardized event emission for lending contract

[dinahmaccodes]

Closes #233

This pull request introduces a comprehensive event logging system to the borrowing contract, allowing key actions such as borrowing, repaying, and liquidating loans to be tracked via structured events. These changes improve contract transparency, enable easier integration with off-chain systems, and provide better observability for users and developers. The implementation includes new event types, emits events at relevant contract actions, and updates test snapshots to validate event outputs.

Event system enhancements:

• Added four new event structs (BorrowEvent, RepayEvent, LiquidationEvent, and InterestAccrualEvent) to define the structure of contract events for loan actions in lib.rs.
• Integrated event emission in contract logic: now emits a borrow event when a loan is created, a repay event when a loan is repaid, and a liquidation event when a loan is liquidated. [1] [2] [3]

Testing and validation:

• Updated test snapshots to include the new event outputs for borrowing, repaying, and liquidating loans, ensuring that event emission is correctly validated in various scenarios. [1] [2] [3] [4] [5] [6] [7]

Codebase improvements:

• Refactored imports in lib.rs to include symbol_short for event topic encoding and improved clarity in loan creation logic by using .clone() for struct fields. [1] [2]

These changes lay the foundation for robust contract event tracking and pave the way for future improvements in analytics and off-chain integrations.

[ONEONUORA]

Great job @dinahmaccodes