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/unit/test_plugin.c

@@ -0,0 +1,53 @@
+#include "naut/event.h"
+#include "naut/plugin.h"
+#include "naut/rpc.h"
+#include "test.h"
+
+#include <string.h>
+
+#ifndef NAUT_EXAMPLE_PLUGIN
+#define NAUT_EXAMPLE_PLUGIN "naut_example.so"
+#endif
+
+int main(void) {
+    naut_event_bus *events = naut_event_bus_create();
+    naut_rpc_registry *rpc = naut_rpc_registry_create();
+    naut_plugin_manager *plugins =
+        naut_plugin_manager_create(rpc, events);
+    CHECK(events && rpc && plugins);
+    CHECK(naut_plugin_load(plugins, NAUT_EXAMPLE_PLUGIN) == NAUT_OK);
+    CHECK_EQ(naut_plugin_count(plugins), 1);
+    CHECK(strcmp(naut_plugin_name(plugins, 0), "example") == 0);
+    CHECK_EQ(naut_plugin_storage_count(plugins), 1);
+
+    const naut_storage_backend_v1 *backend =
+        naut_plugin_storage_backend(plugins, "memory");
+    CHECK(backend != NULL);
+    naut_err error;
+    void *storage = backend->open("", &error);
+    CHECK(storage && error == NAUT_OK);
+    const char value[] = "plugin-storage";
+    char result[sizeof value];
+    CHECK(backend->write(storage, 17, value, sizeof value) == NAUT_OK);
+    CHECK(backend->read(storage, 17, result, sizeof result) == NAUT_OK);
+    CHECK(memcmp(value, result, sizeof value) == 0);
+    backend->close(storage);
+
+    naut_event event = {
+        .type = NAUT_EVENT_TORRENT_FINISHED,
+        .torrent_id = 9,
+    };
+    naut_event_emit(events, &event);
+    json_t *reply = naut_rpc_dispatch(
+        rpc, "example.events", json_null(), &error);
+    CHECK(error == NAUT_OK && reply);
+    CHECK(json_integer_value(json_object_get(reply, "finished")) == 1);
+    json_decref(reply);
+
+    naut_plugin_manager_destroy(plugins);
+    reply = naut_rpc_dispatch(rpc, "example.events", json_null(), &error);
+    CHECK(reply == NULL && error == NAUT_ERR_INVAL);
+    naut_rpc_registry_destroy(rpc);
+    naut_event_bus_destroy(events);
+    TEST_MAIN_END();
+}