feat: add Phase 1 constraint solver addon, move prior content to GNN/

- Move existing OndselSolver, GNN ML layer, and tooling into GNN/
  directory for integration in later phases
- Add Create addon scaffold: package.xml, Init.py
- Add expression DAG with eval, symbolic diff, simplification
- Add parameter table with fixed/free variable tracking
- Add quaternion rotation as polynomial Expr trees
- Add RigidBody entity (7 DOF: position + unit quaternion)
- Add constraint classes: Coincident, DistancePointPoint, Fixed
- Add Newton-Raphson solver with symbolic Jacobian + numpy lstsq
- Add pre-solve passes: substitution + single-equation
- Add DOF counting via Jacobian SVD rank
- Add KindredSolver IKCSolver bridge for kcsolve integration
- Add 82 unit tests covering all modules

Registers as 'kindred' solver via kcsolve.register_solver() when
loaded by Create's addon_loader.

GNN/OndselSolver/BasicUserFunction.cpp

@@ -0,0 +1,23 @@
+/***************************************************************************
+ *   Copyright (c) 2023 Ondsel, Inc.                                       *
+ *                                                                         *
+ *   This file is part of OndselSolver.                                    *
+ *                                                                         *
+ *   See LICENSE file for details about copyright.                         *
+ ***************************************************************************/
+ 
+#include "BasicUserFunction.h"
+#include "CREATE.h"
+#include "Units.h"
+
+using namespace MbD;
+
+MbD::BasicUserFunction::BasicUserFunction(const std::string& expression, double myUnt) : funcText(expression), myUnit(myUnt)
+{
+	units = std::make_shared<Units>();
+}
+
+void MbD::BasicUserFunction::initialize()
+{
+	units = CREATE<Units>::With();
+}