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.

OptimizedSearch.h

@@ -0,0 +1,27 @@
+// OptimizedSearch.h - Boyer–Moore (bad character) based substring search
+#ifndef KTE_OPTIMIZED_SEARCH_H
+#define KTE_OPTIMIZED_SEARCH_H
+
+#include <array>
+#include <cstddef>
+#include <string>
+#include <vector>
+
+class OptimizedSearch {
+public:
+	OptimizedSearch() = default;
+
+	// Find first occurrence at or after start. Returns npos if not found.
+	std::size_t find_first(const std::string &text, const std::string &pattern, std::size_t start = 0);
+
+	// Find all non-overlapping matches at or after start. Returns starting indices.
+	std::vector<std::size_t> find_all(const std::string &text, const std::string &pattern, std::size_t start = 0);
+
+private:
+	std::array<int, 256> bad_char_{};
+	std::string last_pat_;
+
+	void build_bad_char(const std::string &pattern);
+};
+
+#endif // KTE_OPTIMIZED_SEARCH_H