Implement a Simple malloc / Free List

Question

## Problem

Sketch a custom `malloc`/`free` over a fixed memory arena: maintain a free list, split and coalesce blocks.

## Example
```
alloc(16), alloc(32), free(first), alloc(16) reuses the freed block
```

## Constraints
- Avoid fragmentation where possible

## What Broadcom looks for
Understanding of heap mechanics, headers, alignment, and coalescing.