Implement an LSM/B-Tree Range Scan

Question

## Problem

Implement an ordered key-value store supporting point lookups and range scans (a B-tree or sorted structure).

## Example
```
put/get; scan(lo, hi) returns ordered keys in range
```

## Constraints
- Efficient range queries

## Approach
Balanced tree or sorted index; discuss B-tree vs LSM trade-offs (read vs write amplification).