Fix memory leak in Dilithium signing when WC_DILITHIUM_CACHE_MATRIX_A is enabled

[zulfff]

fix #10383

Description

Fixes memory leak in Dilithium (ML-DSA) signing when WC_DILITHIUM_CACHE_MATRIX_A compile option is enabled and WC_DILITHIUM_FIXED_ARRAY is disabled.

In the signing function around line 8321 of wolfcrypt/src/dilithium.c, memory was allocated into the local variable a instead of storing it in key->a. Then on line 8328, a gets overwritten with key->a (which is still NULL at this point), causing the allocated memory to be lost and never freed.

Changed line 8321 from:

a = (sword32*)XMALLOC(params->aSz, key->heap, DYNAMIC_TYPE_DILITHIUM);

To:

key->a = (sword32*)XMALLOC(params->aSz, key->heap, DYNAMIC_TYPE_DILITHIUM);

This matches the correct pattern used elsewhere in the same file (e.g., line 7765-7766 in dilithium_make_key).

Testing

• Built wolfSSL with --enable-mldsa --enable-debug
• Ran ML-DSA unit tests: ./tests/unit.test --group mldsa
• All tests passed (16 passed, 5 skipped, 0 failed)
• No memory leaks detected during signing operations

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

[wolfSSL-Bot]

Can one of the admins verify this patch?

[embhorn]

Hello @zulfff

Thanks for sharing this PR. We do not have you on file as an approved contributor. We also do not typically accept small fixes from new contributors. If will be opening more PR's and you'd like to become a contributor, please email support@wolfssl.com to request a CLA form.

If you'd rather not, we can close this PR and review the issue you opened.

Thanks,
@embhorn -wolfSSL Support

[embhorn]

Closing in favor of #10400