Feat/borrowing

[nafsonig]

Summary of Changes

The lending contract lending/src/lib.rs had several duplicate functions that would have caused compilation errors. I removed:

1. The second duplicate get_pool_accounting function
2. An outdated get_interest_rate function that incorrectly tried to read from a non-existent pool
3. An outdated borrow function that had incomplete token transfer logic
4. An incomplete/stray repay function that was cut off mid-implementation

Current State of Key Functions

The contract now maintains only the correct, single implementations of the required functions for the borrowing lifecycle:

• ✅ get_interest_rate - Properly iterates through all pools to find the asset's pool and returns its interest rate
• ✅ borrow - Validates inputs, accrues interest, checks liquidity, and updates pool accounting correctly
• ✅ repay - Processes principal and interest payments, updates accounting properly
• ✅ get_pool_accounting - Single implementation that accrues interest before returning accounting data

These functions are now ready to support the borrowing contract's cross-contract calls for the complete collateralized borrowing lifecycle implementation.

closes #78