Implement memcpy / Reverse a String In-Place

Question

## Problem

Implement `memcpy` handling overlapping regions correctly (i.e., `memmove` semantics), and reverse a C string in place.

## Example
```
memmove with overlap; reverse("hello") -> "olleh"
```

## Constraints
- Handle overlap and null terminator

## Approach
Copy direction depends on src/dst overlap. Discuss why naive memcpy corrupts overlapping ranges.