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]

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