layout: restructure into src/ tests/ android/ scripts/ tools/

- extension/src/{port,platform,codepage} -> src/; native_render -> src/host
  (+ dxt, shaders/); libgr2 -> src/gr2; extension/third_party -> third_party
- extension/tests -> tests/port, libgr2/tests -> tests/gr2
- android-native -> android (build.sh, push-client.sh moved in)
- script -> scripts; tools/40250 -> tools/server; oracle -> tools/granny-oracle;
  perf tools -> tools/perf
- all build trees under build/ (native, release, android, port-gate)
- xrender:: CMake aliases -> mt::; port-map ledger impl paths rewritten

No code changes. ctest 15/15, port_gate macos+android PASS, port_map check 0 errors.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

third_party/cryptopp/gf256.cpp

@@ -0,0 +1,34 @@
+// gf256.cpp - originally written and placed in the public domain by Wei Dai
+
+#include "pch.h"
+#include "gf256.h"
+
+NAMESPACE_BEGIN(CryptoPP)
+
+GF256::Element GF256::Multiply(Element a, Element b) const
+{
+	word result = 0, t = b;
+
+	for (unsigned int i=0; i<8; i++)
+	{
+		result <<= 1;
+		if (result & 0x100)
+			result ^= m_modulus;
+
+		t <<= 1;
+		if (t & 0x100)
+			result ^= a;
+	}
+
+	return (GF256::Element) result;
+}
+
+GF256::Element GF256::MultiplicativeInverse(Element a) const
+{
+	Element result = a;
+	for (int i=1; i<7; i++)
+		result = Multiply(Square(result), a);
+	return Square(result);
+}
+
+NAMESPACE_END