refactor: update contest problem info extraction

[QuBenhao]

add unicode decoding

new contest fit

[Copilot]

Pull Request Overview

Refactors contest problem info extraction by switching from regex-based HTML/script parsing to JSON-driven parsing, adds a Unicode decoding utility, and updates template file access to use relative paths.

• Adds decode_unicode_string to handle JS-encoded Unicode sequences.
• Updates get_contest_problem_info to parse __NEXT_DATA__ JSON instead of regex on HTML and decodes content.
• Changes code templates to load input.json/output.json via Path for relative file access.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
python/utils/str_util.py	Introduces decode_unicode_string for transforming \uXXXX, \n, and \t escapes.
python/lc_libs/contest.py	Replaces regex+BeautifulSoup logic with JSON parsing from __NEXT_DATA__, updates URL.
python/constants/code_templates.py	Switches to Path(__file__).parent for opening JSON files relative to the script.

Comments suppressed due to low confidence (2)

python/utils/str_util.py:36

• Missing docstring: consider adding a brief docstring to decode_unicode_string explaining its behavior, expected input format, and return value.

def decode_unicode_string(s: str) -> str:

python/constants/code_templates.py:228

• Missing import: Path is used here but not imported. Add from pathlib import Path at the top of the file to prevent a NameError.

root_path = Path(__file__).parent