feat: port GIP protocol and auth stack

Port the GIP protocol and authentication layers from medusalix/xone
into the C++ stack:

- crypto: SHA-256/HMAC (CommonCrypto), RSA PKCS#1 (Security.framework),
  and a self-contained P-256 ECDH validated against OpenSSL vectors
- auth: v1 (RSA) and v2 (ECDH) handshake state machine
- gip: header/varint/chunk handling and packet dispatch, with the kernel
  device model replaced by transport + client_listener interfaces

Adds test_crypto, test_auth, and test_gip suites.

Co-Authored-By: deepseek (deepseek/deepseek-v4-pro-0813): ported crypto, auth, and GIP

include/common/log.hpp

@@ -0,0 +1,48 @@
+#pragma once
+
+// ==============================================================================
+// Minimal printf-style logger
+// ==============================================================================
+// Replaces the kernel's dev_dbg/dev_err from medusalix/xone. Writes to
+// stderr; the Swift app layer can redirect or swallow it later.
+// ==============================================================================
+
+#include <cstdarg>
+#include <cstdio>
+
+namespace xone {
+
+enum class log_level {
+    debug = 0,
+    info,
+    warn,
+    error,
+};
+
+inline auto log_msg(log_level level, char const* fmt, ...) -> void
+{
+    char const* tag = "?";
+    switch (level) {
+    case log_level::debug:
+        tag = "debug";
+        break;
+    case log_level::info:
+        tag = "info";
+        break;
+    case log_level::warn:
+        tag = "warn";
+        break;
+    case log_level::error:
+        tag = "error";
+        break;
+    }
+
+    std::fprintf(stderr, "[%s] ", tag);
+    va_list ap;
+    va_start(ap, fmt);
+    std::vfprintf(stderr, fmt, ap);
+    va_end(ap);
+    std::fprintf(stderr, "\n");
+}
+
+} // namespace xone