Improve Security by Using Cryptographically Secure Random Numbers for IV Generation

[kexinoh]

this pull request aims to enhance the security of the encryption process by replacing the non-cryptographically secure random number generation in the get_initialization_vector method with a cryptographically secure alternative.

While maintaining backward compatibility, the changes made in this PR focus on the following:

The use of random.randint for generating the initialization vector (IV) has been replaced with os.urandom to ensure that the IV is generated using a cryptographically secure random number generator.
The default static IV is retained to ensure backward compatibility with existing systems that may rely on this behavior. However, it is strongly recommended to use the new, cryptographically secure random IV generation for all new encryption operations.

These changes will help protect against potential vulnerabilities associated with predictable IVs without breaking existing functionality.