Add self-validation method for CryptoSecrets

[zHd4]

This PR adds a validate() method to the CryptoSecrets class that performs comprehensive validation of cryptographic secrets, ensuring keys and passwords meet security requirements:

• Key is not null/empty and exactly 384-bit (48 bytes) in size
• Password is not null/empty and at least 4 characters long
• Key is not all zeros (preventing nulled/destroyed keys from being used)
• Password contains at least one non-zero character (preventing nulled/destroyed passwords)
• The PR also includes helper utilities (KeyUtils.isKeyNulled() and CharUtils.hasNonZeroChars()), refactors the KEY_SIZE constant to be part of CryptoSecrets, and adds comprehensive unit tests for all new validation logic