feat(arbitrage): Introduce trade counter & test mode flag with full NatSpec documentation

[0xRiz0]

Description

This PR enhances the TestArbitrage contract with two important state variables designed to support tracking, analytics, and controlled simulation flows.

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✅ Key Additions

Variable	Type	Purpose
tradeCounter	uint256	Auto-incrementing counter used to uniquely identify each executed trade
testMode	bool	Toggle that enables special testing/simulation-only logic without affecting production execution

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📦 Code Changes

/// @notice Counter for trade IDs
/// @dev Incremented for each new trade
uint256 public tradeCounter;

/// @notice Test mode flag for simulation purposes
/// @dev When true, enables additional testing features
bool public testMode;