(C2 Main) (NEW): Walrus and Sui gas cost module

[domenicodev]

Closes: #

Summary

Module containing lesson material, hands-on code and theory for Walrus and Sui gas cost computation, informations and best practices.

Type of Change

• Bug fix (broken example, compilation error, incorrect code)
• New content (lesson, module, exercise)
• Content improvement (clearer explanation, better examples)
• Code update (dependency bump, Move edition migration)
• Scaffold or tooling change
• Documentation update

Affected Modules

C2

Checklist

• Targeted against main branch
• Linked to a GitHub issue
• Move code compiles (sui move build)
• Tests pass (sui move test)
• TypeScript code compiles (if applicable)
• Solution branch updated (if applicable)
• Lesson README is consistent with code changes
• Re-reviewed Files changed in the GitHub PR explorer