Changed o3c.Tensor.arange signature to be like np.arange.

[timohl]

Type

• Bug fix (non-breaking change which fixes an issue): Fixes #
• New feature (non-breaking change which adds functionality). Resolves #
• Breaking change (fix or feature that would cause existing functionality to not work as expected) Resolves #

Motivation and Context

The current signatures of open3d.core.Tensor.arange are not valid:

arange(stop, dtype=None, device=None)
arange(start=None, stop, step=None, dtype=None, device=None)

in the second signature, start has a default value but is before stop.
See The Python Language Reference:

If a parameter has a default value, all following parameters up until the “*” must also have a default value — this is a syntactic restriction that is not expressed by the grammar.

This is how numpy defines arange:

@overload
def arange(  # type: ignore[misc]
    stop: _IntLike_co,
    /, *,
    dtype: None = ...,
    device: None | L["cpu"] = ...,
    like: None | _SupportsArrayFunc = ...,
) -> _1DArray[int, signedinteger[Any]]: ...
@overload
def arange(  # type: ignore[misc]
    start: _IntLike_co,
    stop: _IntLike_co,
    step: _IntLike_co = ...,
    dtype: None = ...,
    *,
    device: None | L["cpu"] = ...,
    like: None | _SupportsArrayFunc = ...,
) -> _1DArray[int, signedinteger[Any]]: ...

(see https://github.com/numpy/numpy/blob/b3ddf2fd33232b8939f48c7c68a61c10257cd0c5/numpy/_core/multiarray.pyi#L769-L786)

Note how start is not optional in the second signature.
Here, optional is not needed, because the first overload handles that case.

Also, it adds /, *, in the first signature and *, in the second.
/ forces all args before to be positional-only and * forces all arguments after to be keyword-only.
In pybind this can be achieved using py::pos_only() and py::kw_only().

Checklist:

• I have run python util/check_style.py --apply to apply Open3D code style
  to my code.
• This PR changes Open3D behavior or adds new functionality.
  • Both C++ (Doxygen) and Python (Sphinx / Google style) documentation is
    updated accordingly.
  • I have added or updated C++ and / or Python unit tests OR included test
    results (e.g. screenshots or numbers) here.
• I will follow up and update the code if CI fails.
• For fork PRs, I have selected Allow edits from maintainers.

Description

This PR changes the signatures to (similar to numpy.arange):

arange(stop, /, *, dtype=None, device=None)
arange(start, stop, step=None, dtype=None, *, device=None)

There is already an unittest for o3c.Tensor.arange: test_arange in python/test/core/test_core.py
The test still succeeds with this change.

However, existing code might break if it does not use dtype or device as a keyword argument, e.g., like this:
o3c.Tensor.arange(2, o3c.int64)
This must now be written as:
o3c.Tensor.arange(2, dtype=o3c.int64)
(which the unit test already does)

This is a fix used in #6917 since mypy would complain about a syntax error in stubs generated by pybind11-stubgen:

mypy examples/python/geometry/triangle_mesh_with_numpy.py 
/home/timohl/projects/Open3D/.venv/lib/python3.10/site-packages/open3d/cpu/pybind/core/__init__.pyi:732: error: non-default argument follows default argument  [syntax]
Found 1 error in 1 file (errors prevented further checking)

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[ssheorey]

Looks good. Thanks @timohl