feat(arbitrage): Introduce TradeInitiated & TradeCompleted lifecycle events

[0xRiz0]

Description

This PR enhances the TestArbitrage contract with full trade lifecycle tracking by introducing two new events:

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✅ Added Events

TradeInitiated

Emitted at the start of an arbitrage attempt, providing complete context on routing and flash loan parameters.

event TradeInitiated(
    uint256 indexed tradeId,
    address indexed tokenIn,
    address indexed tokenOut,
    uint256 flashAmount,
    address router1,
    address router2,
    address initiator
);