Feature/77 implement add liquidity amm contract

[dreamgene]

Closes #77

Summary

Implements the add_liquidity function in the AMM contract, allowing liquidity providers (LPs) to deposit USDC into prediction market pools and receive LP tokens proportional to their pool share.

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File Changed

• contracts/contracts/boxmeout/src/amm.rs

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Changes

• Implemented add_liquidity instruction to accept USDC deposits from LPs
• LP tokens minted proportionally based on current pool share; first provider receives tokens 1:1
• Updated usdc_reserve and k constant after each liquidity deposit
• Emitted LiquidityAdded event with provider, amount, minted tokens, new reserve, and updated k
• Added unit tests covering first provider, proportional minting, reserve updates, and k constant recalculation

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Event Emitted

LiquidityAdded {
    provider: Pubkey,
    usdc_amount: u64,
    lp_tokens_minted: u64,
    new_reserve: u64,
    k: u64,
}

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Acceptance Criteria

• Accept USDC from LP, mint LP tokens proportional to pool share
• Update reserves and k constant
• Emit LiquidityAdded event
• Unit tests

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Testing

• First LP receives tokens 1:1
• Subsequent LPs receive proportional share
• Reserves correctly updated after deposit
• k constant recalculated after liquidity added

cargo test