add basic types and fix cmake

src/lib/config/Formula.h

@@ -0,0 +1,40 @@
+#pragma once
+
+#include <memory>
+#include <string>
+
+// Forward declaration so tinyexpr.h stays out of this header.
+struct te_expr;
+
+// Compiled single-variable expression. The bound variable is named x.
+// Compile once at config load; evaluate many times at simulation time.
+// tinyexpr bakes the address of the bound variable into the compiled tree, so
+// we keep x on the heap to preserve that pointer across moves.
+class Formula
+{
+public:
+    Formula() = default;
+
+    Formula(const Formula&) = delete;
+    Formula& operator=(const Formula&) = delete;
+
+    Formula(Formula&& other) noexcept;
+    Formula& operator=(Formula&& other) noexcept;
+
+    ~Formula();
+
+    // Parses source and returns a ready-to-evaluate Formula.
+    // Throws std::runtime_error with the source and error position on failure.
+    static Formula compile(const std::string& source);
+
+    // Evaluates the expression at the given x. Requires a compiled formula.
+    double evaluate(double x) const;
+
+    const std::string& source() const { return m_source; }
+    bool isValid() const { return m_expr != nullptr; }
+
+private:
+    std::string m_source;
+    std::unique_ptr<double> m_x;
+    te_expr* m_expr = nullptr;
+};