Fix ChaCha20Poly1305 to be singleshot

[embhorn]

Changes Made

wolfcrypt/ciphers.py — ChaCha20Poly1305 class rewritten

Removed (streaming-style interface):

• set_aad(), get_aad() — AAD is now passed directly to encrypt/decrypt
• checkTag() — standalone tag checking
• final() — had bugs (self._native_type instead of self._native_object) and was unreachable anyway
• Mode tracking (_mode, _ENCRYPTION/_DECRYPTION state)
• _native_object / _native_type — no longer needed since we use the one-shot C functions
• _IV, _aad instance state

New interface (matches AesSiv pattern):

• init(self, key) — only takes the key
• encrypt(self, aad, iv, plaintext) → (ciphertext, authTag) — one-shot encryption
• decrypt(self, aad, iv, authTag, ciphertext) → plaintext — one-shot decryption
• _key_sizes fixed to [32] (ChaCha20-Poly1305 requires 256-bit keys per RFC 7539)

tests/test_chacha20poly1305.py — updated tests

• Updated test_encrypt_decrypt to use the new one-shot interface
• Same instance can now be reused for both encrypt and decrypt
• Added test_invalid_key_size and test_decrypt_bad_tag tests
• Removed unused imports (namedtuple)

Fixes #83

[Copilot]

Pull request overview

This PR rewrites the ChaCha20Poly1305 wrapper to use a one-shot (non-streaming) AEAD interface aligned with the existing AesSiv pattern.

Changes:

• Replaced the streaming-style API with one-shot encrypt(aad, iv, plaintext) and decrypt(aad, iv, authTag, ciphertext).
• Enforced RFC 7539 key size by restricting _key_sizes to 32 bytes.
• Updated and expanded tests for the new interface, including invalid key-size and bad-tag cases.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

File	Description
wolfcrypt/ciphers.py	Replaces streaming state with one-shot calls to the underlying wolfCrypt ChaCha20-Poly1305 functions.
tests/test_chacha20poly1305.py	Updates tests to use the new API and adds negative tests for key size and tag verification.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

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