Remove deprecated GenericArray usage

[mullerch]

This pull request refactors the AES-128 encryption code to simplify usage of the aes crate and improve code clarity. The main changes remove unnecessary dependencies on GenericArray, update cipher initialization to use the more idiomatic new_from_slice method, and make minor improvements to buffer handling.

AES-128 cipher usage improvements:

• Replaced manual use of GenericArray with direct use of Aes128::new_from_slice for cipher initialization in src/aes128.rs and src/packets.rs, making the code more concise and idiomatic.
• Updated block creation and encryption to use Block::from and Block::from_mut_slice as appropriate, further simplifying the code and improving readability.

Code clarity and correctness:

• Changed buffer initialization from Vec<u8> to [u8; 16] arrays and replaced clone_from_slice with copy_from_slice for better type safety and clarity in src/packets.rs.
• Updated CMAC initialization to use fully qualified syntax for clarity: <Cmac<Aes128> as Mac>::new_from_slice.

[brocaar]

Thanks @mullerch