Evaluate an arithmetic string

Question

Write `solve(raw: str) -> str` that evaluates one arithmetic expression and returns its integer value as text.

```python
def solve(raw: str) -> str: ...
```

## Requirements

- The expression contains non-negative integers, single spaces, and the operators `+`, `-`, `*`, and `/`. There are no parentheses, no unary minus, and no exponentiation.
- `*` and `/` bind more tightly than `+` and `-`; work left to right inside each precedence level.
- `/` is integer division that truncates toward zero, so `-3/2` truncates to `-1` if a lead-in subtraction makes the intermediate negative.
- Ignore every space and read the run of digits between operators as one number.
- Return the result as a decimal string with no padding and no trailing newline. `run_case` passes `case["stdin"]` to `solve`.
- Assume the input is a well-formed expression; you do not need to report syntax errors.