feat(amm): Introduce removeLiquidity external function with proportional withdrawal & slippage protection

[Neros0]

Description

This PR adds full liquidity withdrawal support to the TestAMMContract by introducing the removeLiquidity external function. This complements the previously implemented addLiquidity function and enables users to safely exit their positions while preserving pool accounting.

---

✅ Key Features

Feature	Description
Proportional Withdrawal	Calculates token amounts based on user’s share of total liquidity
Slippage Protection	Enforces _amount0Min / _amount1Min thresholds to prevent MEV/front-running issues
Reserve & User Accounting	Updates both pool reserves and userLiquidity tracking
Token Transfers	Sends withdrawn tokens back to _user
Event Emission	Emits existing LiquidityRemoved event for indexing

---

🧠 Function Summary

function removeLiquidity(
    bytes32 _marketId,
    address _user,
    uint128 _liquidity,
    uint256 _amount0Min,
    uint256 _amount1Min
)
    external
    returns (uint256 amount0Decreased, uint256 amount1Decreased, uint256 amount0Collected, uint256 amount1Collected)