Add new benchmarks, optimized search, UndoNode pool, and fix horizontal scrolling.

- Added benchmarking for GapBuffer and PieceTable (BufferBench, PerformanceSuite).
- Implemented `OptimizedSearch` using Boyer-Moore (bad character heuristic).
- Introduced `UndoNodePool` for efficient memory management.
- Fixed horizontal scrolling and cursor placement in GUI: ensured cursor visibility and improved accuracy for rendered columns.

test_buffer_correctness.cc

@@ -0,0 +1,102 @@
+// Simple buffer correctness tests comparing GapBuffer and PieceTable to std::string
+#include <cassert>
+#include <cstddef>
+#include <cstring>
+#include <random>
+#include <string>
+#include <vector>
+
+#include "GapBuffer.h"
+#include "PieceTable.h"
+
+
+template<typename Buf>
+static void
+check_equals(const Buf &b, const std::string &ref)
+{
+	assert(b.Size() == ref.size());
+	if (b.Size() == 0)
+		return;
+	const char *p = b.Data();
+	assert(p != nullptr);
+	assert(std::memcmp(p, ref.data(), ref.size()) == 0);
+}
+
+
+template<typename Buf>
+static void
+run_basic_cases()
+{
+	// empty
+	{
+		Buf b;
+		std::string ref;
+		check_equals(b, ref);
+	}
+
+	// append chars
+	{
+		Buf b;
+		std::string ref;
+		for (int i = 0; i < 1000; ++i) {
+			b.AppendChar('a');
+			ref.push_back('a');
+		}
+		check_equals(b, ref);
+	}
+
+	// prepend chars
+	{
+		Buf b;
+		std::string ref;
+		for (int i = 0; i < 1000; ++i) {
+			b.PrependChar('b');
+			ref.insert(ref.begin(), 'b');
+		}
+		check_equals(b, ref);
+	}
+
+	// append/prepend strings
+	{
+		Buf b;
+		std::string ref;
+		const char *hello = "hello";
+		b.Append(hello, 5);
+		ref.append("hello");
+		b.Prepend(hello, 5);
+		ref.insert(0, "hello");
+		check_equals(b, ref);
+	}
+
+	// larger random blocks
+	{
+		std::mt19937 rng(42);
+		std::uniform_int_distribution<int> len_dist(0, 128);
+		std::uniform_int_distribution<int> coin(0, 1);
+		Buf b;
+		std::string ref;
+		for (int step = 0; step < 2000; ++step) {
+			int L = len_dist(rng);
+			std::string payload(L, '\0');
+			for (int i         = 0; i < L; ++i)
+				payload[i] = static_cast<char>('a' + (i % 26));
+			if (coin(rng)) {
+				b.Append(payload.data(), payload.size());
+				ref.append(payload);
+			} else {
+				b.Prepend(payload.data(), payload.size());
+				ref.insert(0, payload);
+			}
+		}
+		check_equals(b, ref);
+	}
+}
+
+
+int
+main()
+{
+	run_basic_cases<GapBuffer>();
+	run_basic_cases<PieceTable>();
+	return 0;
+}