Update version to 1.3.1 and enhance docstring handling

[Artemonim]

Type of Change

• 🐛 Bug Fix: A change that fixes an issue.
• ✨ New Feature: A change that adds new functionality.
• ♻️ Refactor: A code change that neither fixes a bug nor adds a feature.
• 📚 Documentation: Changes to the documentation only.
• ⚙️ CI/CD: Changes to our CI/CD configuration and scripts.
• 🔨 Build: Changes that affect the build system or external dependencies.
• 🎨 Style: Changes that do not affect the meaning of the code (white-space, formatting, etc.).
• ⏪ Revert: Reverts a previous commit.

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Description

Added

• Python Single-Line Docstrings: Implemented support for identifying and merging the generated table of contents with existing single-line Python docstrings ("""docstring""").

Fixed

• Python Docstring Generation: Fixed a critical bug where repeatedly processing a Python file with a manual docstring would cause content duplication. The logic has been reworked to ensure correct placement of the generated table of contents relative to from __future__ import statements and existing docstrings.

CI/CD

• CI dev: The CI pipeline now runs on the dev branch, with Codecov reports limited to master.
• Version check: Added a new check to prevent accidental version bumps in feature branches.

Checklist

• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• New unit tests have been added to cover the changes.
• Manual testing has been performed