[Code scan] Declare IPython dependency for notebook integration

[njzjz]

This issue was found by a Codex global code scan of the repository.

Affected code:

dargs/dargs/notebook.py

Lines 27 to 32 in b4db564

	from IPython.display import HTML, display
	from dargs import Argument, Variant
	from dargs.dargs import _resolve_ref
	__all__ = ["JSON"]

dargs/pyproject.toml

Lines 18 to 22 in b4db564

	dependencies = [
	"typeguard>=4",
	'typing_extensions; python_version < "3.8"',
	]
	requires-python = ">=3.7"

dargs/pyproject.toml

Lines 30 to 43 in b4db564

	[project.optional-dependencies]
	test = [
	"ipython",
	"jsonschema",
	"pyyaml",
	]
	typecheck = [
	"ty==0.0.17",
	"sphinx",
	"ipython",
	]
	yaml = [
	"pyyaml",
	]

dargs/README.md

Lines 28 to 34 in b4db564

	## Additional features
	- [PEP 484](https://peps.python.org/pep-0484/) type annotations
	- Native integration with [Sphinx](https://github.com/sphinx-doc/sphinx), [DP-GUI](https://github.com/deepmodeling/dpgui), and [Jupyter Notebook](https://jupyter.org/)
	- JSON encoder for `Argument` and `Variant` classes
	- Generate [JSON schema](https://json-schema.org/) from an `Argument`, which can be further integrated with JSON editors such as [Visual Studio Code](https://code.visualstudio.com/)
	- Load dict values from external JSON/YAML files via the `$ref` key

Problem:
The README advertises native Jupyter Notebook integration, and dargs.notebook imports IPython.display at module import time. However, IPython is only listed under the test and typecheck extras, not as a runtime dependency or a notebook extra.

Reproducer in a minimal runtime environment without IPython:

from dargs.notebook import JSON

Observed behavior:

ModuleNotFoundError: No module named 'IPython'

Expected behavior:
Either declare a dedicated notebook extra such as dargs[notebook] that includes IPython and document it, or make dargs.notebook fail with a clear optional-dependency message.