Move TCG and vendor command buffers to the heap in small-stack builds

[aidangarske]

Context

WOLFSPDM_DYNAMIC_MEMORY (wolfTPM --enable-smallstack) only heap-allocates the context and the ML-DSA key. The TCG transport and vendor command paths still keep their per-call buffers on the stack, same as wolfTPM master.

Origin

main...wolftpm-core

What is needed

• Allocate the TCG transport and vendor command scratch buffers with XMALLOC under WOLFSPDM_DYNAMIC_MEMORY, freeing on every path.
• Measure peak stack before and after.

Blockers and dependencies

No response

Acceptance criteria

Small-stack Nuvoton and Nations builds pass; valgrind clean; measured stack drop recorded.