fix: drop redundant XMEMSET before XMSS Init

[MarkAtwood]

Bug: In both XMSS sign functions in src/sign-verify/clu_sign.c, the key struct is zeroized with XMEMSET(key, 0, sizeof(XmssKey)) immediately before calling wc_XmssKey_Init(key, HEAP_HINT, 0). This memset is redundant and reorder-fragile.

Fix: wc_XmssKey_Init() already zeroizes the entire struct via ForceZero(key, sizeof(XmssKey)) before setting heap/devId/state (see wolfcrypt/src/wc_xmss.c). The manual XMEMSET is fully redundant, so it is removed at both sites; the comment is kept and annotated. No behavior change — Init self-zeroizes.

Build-verified: compiled the affected translation unit against a wolfSSL install with -DWOLFSSL_HAVE_XMSS (the config where this block is live); compiles clean (exit 0), object shows the expected U wc_XmssKey_Init reference.

Reported by static analysis (Fenrir finding 581).

[Copilot]

Pull request overview

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Removes redundant zero-initialization of XmssKey structs immediately before wc_XmssKey_Init(), relying on the init function’s internal zeroization to avoid reorder-fragility while preserving behavior.

Changes:

• Deleted XMEMSET(key, 0, sizeof(XmssKey)) before wc_XmssKey_Init() in wolfCLU_sign_data_xmss().
• Deleted XMEMSET(key, 0, sizeof(XmssKey)) before wc_XmssKey_Init() in wolfCLU_sign_data_xmssmt().
• Updated the nearby comments to document that wc_XmssKey_Init() zeroizes the struct internally.

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