Python 3.14 support

[petrotiurin]

Installing aisuite with python 3.14 works, but fails on import.

To reproduce:

1. Ensure Python 3.14 is used by running python3 -V
2. python3 -m pip install aisuite
3. python3 -c "import aisuite as ai"

Results in the following stack trace:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
    import aisuite as ai
  File "/Users/petrot/Development/repro/.venv/lib/python3.14/site-packages/aisuite/__init__.py", line 1, in <module>
    from .client import Client
  File "/Users/petrot/Development/repro/.venv/lib/python3.14/site-packages/aisuite/client.py", line 3, in <module>
    from .utils.tools import Tools
  File "/Users/petrot/Development/repro/.venv/lib/python3.14/site-packages/aisuite/utils/tools.py", line 5, in <module>
    from docstring_parser import parse
  File "/Users/petrot/Development/repro/.venv/lib/python3.14/site-packages/docstring_parser/__init__.py", line 14, in <module>
    from .parser import compose, parse, parse_from_object
  File "/Users/petrot/Development/repro/.venv/lib/python3.14/site-packages/docstring_parser/parser.py", line 7, in <module>
    from docstring_parser.attrdoc import add_attribute_docstrings
  File "/Users/petrot/Development/repro/.venv/lib/python3.14/site-packages/docstring_parser/attrdoc.py", line 17, in <module>
    ast.NameConstant: "value",
    ^^^^^^^^^^^^^^^^
AttributeError: module 'ast' has no attribute 'NameConstant'