feat: add generic iterative segment tree class

iter-seg-tree/src/main.cpp

@@ -0,0 +1,14 @@
+#include <iostream>
+#include <vector>
+
+// this isn't ideal
+#include "../include/iter_seg_tree.hpp"
+
+int main() {
+    auto sum = [](int a, int b) { return a + b; };
+
+    std::vector<int> vec = {1, 2, 3, 4};
+    IterSegTree<int> st(vec, sum, 0);
+
+    std::cout << st.query(0, 2) << "\n";
+}