Add lesson-style assignments for lessons 1, 2, & 3

[AntonioCoppe]

Title: Add lesson-style assignments for lessons 1–3

Description:
This PR adds three comprehensive assignment files that provide hands-on practice with FFmpeg-style assembly programming.

Files Added:

• assignments/lesson_01.md – Basic loops and data movement
• assignments/lesson_02.md – Conditional jumps and nested loops
• assignments/lesson_03.md – SIMD operations and advanced techniques

Structure & Content:

• Overview section explaining each lesson’s focus
• Multiple assignments with clear C function signatures
• FFmpeg-style cglobal declarations for proper function setup
• Detailed implementation guidance with specific register usage
• Assembly code blocks with proper syntax highlighting
• Step-by-step instructions for each assignment

Educational Value:
These assignments help students to:

• Master FFmpeg’s calling conventions and register usage
• Practice real-world assembly patterns used in multimedia processing
• Build confidence with SIMD instructions and optimization techniques
• Understand the progression from basic loops to advanced SIMD operations

The assignments are designed to complement the existing lesson content and provide practical exercises that reinforce the theoretical concepts covered in each lesson.