docs: add Marp slides for memory layout appendix

[arinal]

Adds docs/slides-memory-layout.md — a Marp-compatible slide deck covering the same content as appendix-memory-layout.md, reformatted for presentations.

Slides cover:

• Process memory layout (stack, heap, BSS, DATA, TEXT)
• Step-by-step trace of a simple Rust program
• Local variable rule: let → stack, always
• Function calls, CPU registers, and stack frames
• References as plain pointers
• Raw pointers vs safe references
• Heap allocation basics
• Memory layouts for common types (String, Vec, Box, nested)
• Common misconceptions
• Stack vs heap performance
• Optimization tips

How to use:

Install Marp CLI and run:

marp docs/slides-memory-layout.md

Or open in VS Code with the Marp extension.