Add SPDM 1.2 CHUNK_GET message chunking and enable ML-DSA-87 over the wire

[aidangarske]

Adds the SPDM 1.2 large-response chunking engine (CHUNK_GET reassembly) and turns ML-DSA-87 on over the wire — the second item of #10. ML-DSA-87's KEY_EXCHANGE_RSP / CHALLENGE_AUTH / signed MEASUREMENTS (~4.7–4.8 KB) exceed the common DataTransferSize (spdm-emu = 4608 B), so the responder splits them; this reassembles them.

Design (per the lightweight / zero-alloc / fine-grained-macro brief)

• Transparent reassembly hooked into the two transport functions — wolfSPDM_SendReceive (cleartext KEY_EXCHANGE / CHALLENGE) and wolfSPDM_SecuredExchange (encrypted MEASUREMENTS) — so every parser sees a complete logical message and the transcript stays correct.
• Zero dynamic allocation: one fixed chunkBuf[WOLFSPDM_CHUNK_BUF_SIZE] in the context holds a single CHUNK_RESPONSE; the reassembled message lands in the caller's existing buffer (no new buffers grow; ctx 72496 B < the 73728 B cap).
• Fine-grained gates: WOLFSPDM_HAVE_CHUNK (--disable-chunking), WOLFSPDM_CHUNK_BUF_SIZE (MTU/transport size — lower it for constrained devices), WOLFSPDM_CHUNK_NO_SECURED (drop just the encrypted path), WOLFSPDM_CHUNK_MAX_CHUNKS.
• Authoritative wire values (DSP0274 Sec. 10.27, cross-checked vs libspdm): CHUNK_GET=0x86, CHUNK_RESPONSE=0x06, CHUNK_CAP=0x00020000, ERROR(LargeResponse)=0x0F, Handle at byte 4, u16-vs-u32 ChunkSeqNo by version.

Testing

• make check: 70 (ML-DSA + chunk) / 65 (chunk, no ML-DSA) / 64 (both disabled) — the gates compile cleanly in/out. New test_chunk_reassemble drives the reassembler with a mock multi-chunk transport and a negative (oversized) case.
• Full strict build clean (-Wall -Wextra -Wpedantic -Werror -Wconversion -Wshadow); zero allocations in src/spdm_chunk.c; no bare-scope blocks.
• CI: the PQC interop matrix now runs ML-DSA-44/65/87 × session/measurements/challenge × (ubuntu 22.04/24.04 x64 + 24.04 aarch64) × dynamic-mem — 87 exercises both the cleartext and secured chunk paths.

New file / docs

• src/spdm_chunk.c (the reassembler) + a Message Chunking wiki page; ML-DSA-87 docs updated (no longer "follow-on").