Protential ReDoS vulnerability in `docstring.py`

[ShangzhiXu]

Describe the bug

Describe the bug
Hi team, thanks for your great work! I think I found a small vulnerability that might lead to DDoS in the system
At line 27 in docstring.py
the regex _google_typed_arg_regex = re.compile(r'(.+?)\(\s*(.*[^\s]+)\s*\)') is vulnerable to ReDoS when it is used in
match = _google_typed_arg_regex.match(before)

How to Reproduce

To Reproduce
I have a test file here and can be run directly

from sphinx.ext.napoleon import Config
from sphinx.ext.napoleon.docstring import GoogleDocstring
import time 

for i in range(500, 2500, 500):
    attack_string = ' ('  + '(' * 2 * i
    google_style_docstring = f"""
brief summary
Args:
    {attack_string}
"""
    start_time = time.time()
    napoleon_config = Config(napoleon_use_param=True, napoleon_use_rtype=True)
    parsed_docstring = GoogleDocstring(google_style_docstring, config=napoleon_config)
    end_time = time.time()
    print(f"i: {i}, Time taken: {end_time - start_time} seconds")

The result is like this

i: 500, Time taken: 4.026143550872803 seconds
i: 1000, Time taken: 32.2109649181366 seconds
i: 1500, Time taken: 109.16966938972473 seconds
i: 2000, Time taken: 258.61019134521484 seconds

As we can see, with around 4k chars, the string can cost the system to hang for around 5 mins. It might lead to some some DDoS or high CPU consumption in real-world scenarios where sphinx is used to parse user input code.

Expected behavior
I think we can add a limit like replace .*? with .{0,200}? ? Maybe it can help to solve the recursion problem.

The core of the problem lies within (.+?)\(\s*(.*[^\s]+). The constructs like (.+?) and .* tend to eagerly match strings, leading to massive recursion and backtracking when faced with malicious input.

I tested a modification of the regex, and the performance improved significantly:

# after modify it to r'(.{0,200}?)\(\s*(.{0,200}[^\s]+)\s*\)'
i: 1000, Time taken: 0.4651494026184082 seconds
i: 2000, Time taken: 0.9634008407592773 seconds
i: 3000, Time taken: 1.4529836177825928 seconds
i: 4000, Time taken: 1.9484753608703613 seconds

Environment Information

lastest version pf sphinx, Linux system, 128 core, 32GB memory

Sphinx extensions

Additional context

No response