Update CHANGELOG.md

Author: Amxx

CHANGELOG.md

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-## XX-XX-XXXX
+## 31-01-2025
+
+- `PaymasterCore`: Add a simple ERC-4337 paymaster implementation with minimal logic.
+- `PaymasterSigner`: Extension of `PaymasterCore` that approves sponsoring of user operation based on a cryptographic signature verified by the paymaster.
+
+## 15-01-2025
 
 - `AccountCore`: Add an internal `_validateUserOp` function to validate user operations.
 - `AccountERC7579`: Extension of `AccountCore` that implements support for ERC-7579 modules of type executor, validator, and fallback handler.