The encrypt_padded_mut API requires the buffer to be large enough to
hold the padded ciphertext. The tests were using plaintext.to_vec() which
only allocated plaintext.len() bytes, insufficient for padding.
Changed pattern:
- Before: plaintext.to_vec() (insufficient space)
- After: vec![0u8; plaintext.len() + 16] with copy_from_slice
Also fixed incorrect usage: encrypt_padded_mut returns Result<(), Error>,
not a length. Use data_copy.len() directly for ciphertext length.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
7ffb1a729f