refactor(ets): extract ET/ETS into own package, add rigorous dh/mdh split()

CMakeLists.txt

@@ -30,17 +30,17 @@ target_include_directories(_frne_c PRIVATE
 
 # ---------------------------------------------------------------------------
 # _fknm_c — forward kinematics, Jacobian, Hessian, IK
-# Eigen is vendored as header-only in src/roboticstoolbox/robot/cpp-extensions/Eigen/
+# Eigen is vendored as header-only in src/roboticstoolbox/ets/cpp-extensions/Eigen/
 # fknm_nb.cpp is the nanobind glue; maths lives in methods/ik/linalg.
 # ---------------------------------------------------------------------------
 nanobind_add_module(_fknm_c
-    src/roboticstoolbox/robot/cpp-extensions/methods.cpp
-    src/roboticstoolbox/robot/cpp-extensions/ik.cpp
-    src/roboticstoolbox/robot/cpp-extensions/linalg.cpp
-    src/roboticstoolbox/robot/cpp-extensions/fknm_nb.cpp
+    src/roboticstoolbox/ets/cpp-extensions/methods.cpp
+    src/roboticstoolbox/ets/cpp-extensions/ik.cpp
+    src/roboticstoolbox/ets/cpp-extensions/linalg.cpp
+    src/roboticstoolbox/ets/cpp-extensions/fknm_nb.cpp
 )
 target_include_directories(_fknm_c PRIVATE
-    src/roboticstoolbox/robot/cpp-extensions
+    src/roboticstoolbox/ets/cpp-extensions
 )
 
 install(TARGETS _frne_c _fknm_c DESTINATION roboticstoolbox)

src/roboticstoolbox/backends/PyPlot/RobotPlot.py

@@ -169,11 +169,11 @@ def draw(self):
                 elif link.isjoint:
                     Tj = T[link.number]
                     R = Tj.R
-                    if link.v.axis[1] == "z":
+                    if link.v.ax == "z":
                         direction = R[:, 2]  # z direction
-                    elif link.v.axis[1] == "y":
+                    elif link.v.ax == "y":
                         direction = R[:, 1]  # y direction
-                    elif link.v.axis[1] == "x":
+                    elif link.v.ax == "x":
                         direction = R[:, 0]  #  direction
 
                 if direction is not None: