aead: zeroize byte-array plaintext when forwarded through encrypt_bytes_array default

[coderdan]

The default impl of Cipher::encrypt_bytes_array in packages/aead/src/cipher.rs calls .to_vec() on the input array before forwarding to encrypt_bytes_vec. We should verify what to_vec does internally and ensure the original stack array is zeroized before drop — otherwise sensitive bytes may linger on the stack after the cipher returns.

See packages/aead/src/cipher.rs (in Cipher::encrypt_bytes_array).

Tracked from PR #148.