Fix AES-CTS one-block and split-init IV handling

[gasbytes]

• In wp_aes_cts_encrypt/wp_aes_cts_decrypt handle an input of exactly one block as plain CBC;
• In wp_aes_stream_init pass ctx->iv to wc_AesSetKey, which is the cached iv from the wolfprovider context;

Added associated regression test for each change (test_aes128_cts_one_block and test_aes128_split_init respectively).

[Copilot]

Pull request overview

This PR fixes two AES-CTS correctness issues in the wolfProvider AES stream implementation: (1) handling CTS for exactly one block, and (2) ensuring split-init sequences correctly preserve/use the IV when the key is set in a separate init call. It also adds targeted regression tests to prevent both issues from recurring.

Changes:

• Treat AES-CTS input of exactly one block as plain CBC (encrypt/decrypt) to match OpenSSL behavior and avoid out-of-bounds behavior.
• Update AES stream initialization to pass the cached ctx->iv into wc_AesSetKey so split init sequences keep the correct IV.
• Add regression tests for one-block CTS and split-init IV handling.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/wp_aes_stream.c	Adjusts key setup IV handling and adds special-case CTS logic for one-block inputs.
test/test_cipher.c	Adds regression tests covering one-block CTS behavior and split-init IV behavior.
test/unit.c	Registers the new unit tests in the test case table.
test/unit.h	Declares prototypes for the new unit tests.

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