- use a dict to map string name to int
- name the parameter axis_type rather than joint_type

…e renames

- Drop UserList in favour of MutableSequence; implement the five required
  abstract methods and delegate to self._data (plain list).
- Add _dirties_fknm decorator; marks _fknm_stale on any mutation so the C
  handle is rebuilt lazily on first use rather than eagerly on every change.
- _copy_to_cpp replaces the old _building context-manager pattern.
- Add __repr__ and __eq__ to BaseETS (MutableSequence provides neither).
- ETS/ETS2 insert() signature now matches MutableSequence: (index, value).
  append() is inherited and works via insert(len, value).
- split() wraps each segment in self.__class__() instead of returning raw slices.
- ETS/ETS2 __init__ raises TypeError for unrecognised arg types (was silent).
- ET.__axis_to_number: use dict.get(axis, 0) to handle SE3 axis gracefully.
- DHRobot: _rne_ob → _frne, _init_rne → _copy_to_cpp, _dynchanged → _frne_stale;
  lazy rebuild at top of rne() removes the old @_check_rne decorator.
- Link/DHLink: _listen_dyn → _dirties_frne; wrapper renamed to match.
- Update test_insert in test_ETS.py and test_ETS2.py for new insert API.

657/660 tests pass; 3 pre-existing URDF/xacro failures unrelated to this change.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Rewrites both C extension glue layers to use nanobind instead of the old
CPython API, eliminating manual reference counting and PyCapsule memory
management.

Key changes in fknm_nb.cpp:
- EigenRef4d (dynamic-stride Ref) for 4×4 matrix inputs (base, tool, Tep):
  accepts C-contiguous, F-contiguous, or any-stride numpy arrays without
  Python-side layout conversion
- EigenRefJd for 6×n Jacobian inputs: fixes hessian corruption when J0
  comes from DHRobot.jacob0() (C-contiguous) vs ETS.jacob0() (F-contiguous)
- dcarray (nb::c_contig) for q vectors; nanobind enforces stride-1 access
- Stride fix: nanobind ndarray strides are in elements, not bytes; corrected
  make_2d_F strides from {sizeof(double), n*sizeof(double)} to {1, n}
- ET_update: bool params (nanobind rejects Python bool where int expected)

Key changes in frne_nb.cpp:
- RobotObj wrapper with proper RAII destructor (no PyCapsule null-destructor)

Key changes in fknm.py facade:
- ET_init/ET_update catch TypeError for symbolic (object-dtype) inputs
- _to_q_array: np.ascontiguousarray for q (handles list/tuple/non-contiguous)
- _to_f_array: np.asarray for SE3 → ndarray (Eigen::Ref handles layout)
- _ik_args_se3: SE3 → ndarray conversion only (no contiguity enforcement)

Key change in DHRobot.rne():
- np.ascontiguousarray(q/qd/qdd) before frne loop; trajectory slices from
  np.c_[...].T are non-contiguous, causing wrong results with stride-1 C code

All 558 non-GUI tests pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

…import

Complete Phase 3 cleanup: delete the legacy CPython-API sources
(fknm.cpp, fknm.h, frne.c) superseded by the nanobind port, and
relocate what remains to reflect that fknm/frne are robot
kinematics/dynamics internals, not general package-level modules:

- move fknm.py/frne.py facades from top-level roboticstoolbox/
  into robot/
- rename+move the C++/C source dir core/ -> robot/cpp-extensions/
  and update CMakeLists.txt paths (never a Python package, so this
  is build-config only; compiled _fknm_c/_frne_c still install to
  the top-level roboticstoolbox package)
- flesh out robot/cpp-extensions/README.md: synopsis, how the
  lazy-serialization/@_dirties_fknm/@_dirties_frne pattern works,
  corrected column-major gotcha, updated file table

Moving fknm.py under robot/ made tools/p_servo.py's module-level
import of Angle_Axis force robot/__init__.py to run before
tools/__init__.py finished initializing, since roboticstoolbox/
loads tools before robot and robot depends on tools at module
scope. Fix: defer the import inside angle_axis() (lazy import),
and have Dynamics.py/DHRobot.py pull rtb_get_param/rtb_set_param
directly from roboticstoolbox.tools.params instead of the
top-level package, decoupling from init order.

Document the lazy-import workaround as tech debt (proper fix is
moving p_servo.py into robot/ itself).

656 tests passing, 0 failed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

TEMPORARY, for CI validation only — revert before merging. rtb-data
hasn't been republished to PyPI since data files were added to main
(publishing now would break existing installs pinned to a version
that doesn't expect these changes). Points at the git subdirectory
instead so CI can validate against current data without a real
release.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

…earlier GH-side update-branch merge)

This reverts commit 6dcfc62.