Accrue tests

[MishaShWoof]

Accrue Tests

accrueAccount test suite — added a dedicated set of tests covering the accrueAccount function, verifying correct behavior across various collateralization states.

[VladyslavPerederWoof]

1. accrueAccount idempotency within the same block
   Calling accrueAccount twice in the same block should be a pure no-op (timeElapsed = 0). Not tested.

2. accrueAccount on one user after global state was advanced by another user's action
   Pattern: bob's supply/withdraw triggers accrueInternal (global), updating lastAccrualTime. Then accrueAccount(alice) is called. Alice's baseTrackingAccrued should update based on the delta between totals.trackingSupplyIndex and alice.baseTrackingIndex. No test isolates this sequence explicitly.

3. balanceOf / borrowBalanceOf increasing over time
   The test verifies userBasic.principal is unchanged after accrue (correct — principal is fixed). But there is no test confirming that balanceOf(alice) (which calls presentValueSupply(baseSupplyIndex, principal)) actually returns a larger value after the index grows, i.e., that supplier earned interest is reflected in their balance.

4. lastAccrualTime after accrueAccount vs. state-changing operations
   accrueInternal updates lastAccrualTime. The test checks lastAccrualTime after supply (line 264-268) but never after a standalone accrueAccount. There's no explicit assertion that lastAccrualTime = block.timestamp after accrueAccount.