Add combined Python + R notebooks with section-level comparison tables

[draprar]

Add combined Python + R notebooks with section-level comparison tables

Summary

This PR introduces a unified learning layer in the form of python_R notebooks, where Python and R implementations are presented side by side. Each major section is supplemented with comparison tables highlighting conceptual and syntactic differences between both approaches.

Changes

• Added new python_R/ directory with combined notebooks organized per chapter/section
• Merged Python and R content into a parallel structure for easier comparison
• Introduced comparison tables at the end of each major section:
  • Python vs R syntax equivalents
  • Conceptual mapping between approaches
  • Practical notes on usage differences and interpretation
• Preserved original repository structure:
  • No changes to existing python/ notebooks
  • No changes to existing R/ notebooks
• Applied minor fixes where required to ensure code execution consistency and correct runtime behavior
• All additions are non-destructive and primarily additive, with limited corrective adjustments where necessary

Motivation

The goal of this change is to improve learning efficiency by:

• enabling direct comparison between Python and R implementations
• reducing context switching between separate notebook structures
• reinforcing statistical and data science concepts through a dual-language perspective
• improving retention through structured side-by-side analysis

Design decisions

• Original separation of Python and R notebooks is intentionally preserved
• The new layer acts as a learning overlay rather than a refactor or replacement
• Fixes were applied only where necessary to ensure notebooks run correctly and consistently
• Focus remains on clarity, correctness, and comparison rather than redesign of original material

Notes

• This PR is educational in nature with minor corrective fixes
• No major architectural or structural changes were introduced
• Intent is to preserve original content while ensuring functional correctness in the combined layer