chore: implementing interfaces from #71

src/interfaces/multipliers/DynamicNFTMultiplier.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.22;
+
+import "@openzeppelin/contracts/token/ERC721/IERC721.sol";
+import "./INFTMultiplier.sol";
+
+/// @title Dynamic NFT Multiplier
+/// @notice This contract provides a dynamic multiplying factor for users based on NFT ownership
+/// @dev Implements the INFTMultiplier interface
+contract DynamicNFTMultiplier is INFTMultiplier {
+    /// @notice The address of the NFT contract
+    IERC721 public immutable NFTAddress;
+
+    /// @notice Mapping of user addresses to their multiplying factors
+    mapping(address => uint256) public userToFactor;
+
+    /// @notice Mapping of user addresses to the validity period of their multiplying factors
+    mapping(address => uint256) public userToValidity;
+
+    /// @notice Constructs the DynamicNFTMultiplier contract
+    /// @param _nftAddress The address of the NFT contract to check for ownership
+    constructor(IERC721 _nftAddress) {
+        NFTAddress = _nftAddress;
+    }
+
+    /// @notice Get the multiplying factor for a user
+    /// @param user The address of the user
+    /// @return The multiplying factor if the user has an NFT, 0 otherwise
+    function getMultiplyingFactor(address user) external view override returns (uint256) {
+        return hasNFT(user) ? userToFactor[user] : 0;
+    }
+
+    /// @notice Get the validity period for a user's factor
+    /// @param user The address of the user
+    /// @return The timestamp until which the user's factor is valid
+    function validUntil(address user) external view override returns (uint256) {
+        return userToValidity[user];
+    }
+
+    /// @notice Check if a user owns an NFT
+    /// @param user The address of the user to check
+    /// @return True if the user owns at least one NFT, false otherwise
+    function hasNFT(address user) public view override returns (bool) {
+        return NFTAddress.balanceOf(user) > 0;
+    }
+}

src/interfaces/multipliers/INFTMultiplier.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.22;
+
+import "@openzeppelin/contracts/token/ERC721/IERC721.sol";
+import {IMultiplier} from "src/interfaces/multipliers/IMultiplier.sol";
+
+/// @title NFT Multiplier Interface
+/// @notice Interface for contracts that provide multiplying factors based on NFT ownership
+/// @dev Extends the IMultiplier interface with NFT-specific functionality
+interface INFTMultiplier is IMultiplier {
+    /// @notice Get the address of the NFT contract
+    /// @return The address of the NFT contract used for checking ownership
+    function NFTAddress() external view returns (IERC721);
+
+    /// @notice Check if a user owns an NFT
+    /// @param user The address of the user to check
+    /// @return True if the user owns at least one NFT, false otherwise
+    function hasNFT(address user) external view returns (bool);
+}