Initial commit: Naut-Torrent — from-scratch 10 GbE BitTorrent client

A maintainable, extensible BitTorrent client (C11, Linux/io_uring) targeting
10 GbE saturation. All torrent functionality is built from scratch; liburing
is the only linked third-party dependency on the data path.

Implements Phases 1-7 of the roadmap:
- core: page-aligned buffer pool, MPMC/Treiber queues, bitfields, worker pool
- crypto: SHA-1/256 (SHA-NI + scalar), Merkle (BEP-52), RC4 (MSE)
- bencode/metainfo: zero-copy parser, v1/v2/hybrid .torrent + magnet
- peer: sans-IO wire codec, MSE/PE handshake state machine, BEP-10, ut_metadata, PEX
- piece/storage: block-level multi-peer engine, rarest-first + endgame,
  per-file completion events + single-file relocate (move-as-you-finish)
- tracker/dht: HTTP + UDP (BEP-15) trackers, BEP-5 KRPC iterative lookup
- platform: io_uring reactor (SQPOLL, registered buffers, SEND_ZC)
- surface: versioned RPC, native plugin ABI, sandboxed Lua scripting, nautd/nautctl

Verified against libtorrent (single/multi/hybrid, MSE, magnet-via-DHT, swarm);
unit + interop tests green; ASan/UBSan/TSan clean. Scripting reference in
docs/scripting.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/fixtures/generate.py

@@ -0,0 +1,40 @@
+import libtorrent as lt, os, hashlib, shutil
+
+root = "tests/fixtures"
+data = os.path.join(root, "data")
+shutil.rmtree(data, ignore_errors=True)
+os.makedirs(os.path.join(data, "multi", "sub"), exist_ok=True)
+
+# deterministic content
+with open(os.path.join(data, "single.bin"), "wb") as f:
+    f.write(bytes((i*131+7) & 0xff for i in range(200000)))
+with open(os.path.join(data, "multi", "a.txt"), "wb") as f:
+    f.write(b"hello naut " * 5000)
+with open(os.path.join(data, "multi", "sub", "b.dat"), "wb") as f:
+    f.write(bytes((i*7) & 0xff for i in range(90000)))
+
+def make(name, src, flags):
+    fs = lt.file_storage()
+    lt.add_files(fs, src)
+    t = lt.create_torrent(fs, piece_size=16384, flags=flags)
+    parent = os.path.dirname(src) if os.path.isfile(src) else os.path.dirname(src.rstrip("/"))
+    t.add_tracker("http://tracker.example.com:8080/announce", 0)
+    t.add_tracker("udp://tracker.example.com:8080", 1)
+    lt.set_piece_hashes(t, parent)
+    ent = t.generate()
+    blob = lt.bencode(ent)
+    path = os.path.join(root, name)
+    with open(path, "wb") as f: f.write(blob)
+    ti = lt.torrent_info(ent)
+    ih = ti.info_hashes()
+    v1 = str(ih.v1) if ih.has_v1() else "-"
+    v2 = str(ih.v2) if ih.has_v2() else "-"
+    print(f"{name}\tv1={v1}\tv2={v2}\tpieces={ti.num_pieces()}\tsize={ti.total_size()}")
+    return path
+
+V1 = lt.create_torrent.v1_only
+V2 = lt.create_torrent.v2_only
+make("single_v1.torrent", os.path.join(data, "single.bin"), V1)
+make("multi_v1.torrent",  os.path.join(data, "multi"), V1)
+make("hybrid.torrent",    os.path.join(data, "multi"), 0)
+make("v2.torrent",        os.path.join(data, "multi"), V2)