Updating content of session 3

[taicoding]

• Refining the explanation of key concepts
• Adding a concise summary of the different method types
• Enhancing the formulation of the challenges for better understanding

[Copilot]

Pull Request Overview

This PR updates the content for session 3 of the Python Study Group OOP course, focusing on methods and object behavior. The updates include refined explanations of key concepts, a summary of method types, and enhanced challenge formulations for better understanding.

• Added comprehensive content for session 3 covering methods, decorators, and special methods
• Standardized syntax highlighting theme across all sessions
• Created new session 3 with complete HTML structure and extensive markdown content

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
plugin/highlight/atom-one-dark-reasonable.css	New CSS file for consistent syntax highlighting theme
index.html	Added navigation link for session 3
content/sesion03/index.html	New HTML structure for session 3 presentation
content/sesion03/Readme.md	Comprehensive markdown content covering methods, behavior, and exercises
content/sesion02/index.html	Updated to use consistent syntax highlighting theme
content/sesion01/index.html	Updated to use consistent syntax highlighting theme

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