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/ExternalSystem.cpp

@@ -0,0 +1,97 @@
+/***************************************************************************
+ *   Copyright (c) 2023 Ondsel, Inc.                                       *
+ *                                                                         *
+ *   This file is part of OndselSolver.                                    *
+ *                                                                         *
+ *   See LICENSE file for details about copyright.                         *
+ ***************************************************************************/
+ 
+#include "ExternalSystem.h"
+#include "CADSystem.h"
+#include "ASMTAssembly.h"
+//#include <Mod/Assembly/App/AssemblyObject.h>
+#include "System.h"
+
+using namespace MbD;
+
+void MbD::ExternalSystem::preMbDrun(std::shared_ptr<System> mbdSys)
+{
+	if (cadSystem) {
+		cadSystem->preMbDrun(mbdSys);
+	}
+    else if (asmtAssembly) {
+        asmtAssembly->preMbDrun(mbdSys);
+        //asmtAssembly->externalSystem->preMbDrun(mbdSys);
+    }
+    else if (freecadAssemblyObject) {
+        //freecadAssemblyObject->preMbDrun();
+    }
+    else {
+		throw SimulationStoppingError("To be implemented.");
+	}
+}
+
+void MbD::ExternalSystem::preMbDrunDragStep(std::shared_ptr<System> mbdSys, std::shared_ptr<std::vector<std::shared_ptr<Part>>> dragParts)
+{
+	asmtAssembly->preMbDrunDragStep(mbdSys, dragParts);
+}
+
+void MbD::ExternalSystem::updateFromMbD()
+{
+	if (cadSystem) {
+		cadSystem->updateFromMbD();
+	}
+	else if (asmtAssembly) {
+		asmtAssembly->updateFromMbD();
+	}
+    else if (freecadAssemblyObject) {
+        //freecadAssemblyObject->updateFromMbD();
+    }
+    else {
+		throw SimulationStoppingError("To be implemented.");
+	}
+}
+
+void MbD::ExternalSystem::outputFor(AnalysisType type)
+{
+	if (cadSystem) {
+		cadSystem->updateFromMbD();
+	}
+	else if (asmtAssembly) {
+		asmtAssembly->updateFromMbD();
+		asmtAssembly->compareResults(type);
+		asmtAssembly->outputResults(type);
+        //asmtAssembly->externalSystem->outputFor(type);
+    }
+    else if (freecadAssemblyObject) {
+        //freecadAssemblyObject->outputResults(type);
+    }
+    else {
+		throw SimulationStoppingError("To be implemented.");
+	}
+}
+
+void MbD::ExternalSystem::logString(const std::string& str)
+{
+	std::cout << str << std::endl;
+}
+
+void MbD::ExternalSystem::logString(double)
+{
+	throw SimulationStoppingError("To be implemented.");
+}
+
+void MbD::ExternalSystem::runOndselPiston()
+{
+	throw SimulationStoppingError("To be implemented.");
+}
+
+void MbD::ExternalSystem::runPiston()
+{
+	throw SimulationStoppingError("To be implemented.");
+}
+
+void MbD::ExternalSystem::postMbDrun()
+{
+	//Do nothing
+}