Tightest slice covering a character multiset

Question

Find the shortest contiguous slice of a source string that contains every character of a required multiset with at least the required multiplicity, and return that slice.

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

## Requirements

- Line 1 is the source string. Line 2 lists the required characters.
- The chosen slice must be contiguous and must contain each required character at least as many times as it appears on line 2.
- Compare slices by length. When several slices tie for the shortest length, return the one that begins earliest.
- If no slice qualifies, return an empty string.
- Matching is case-sensitive.
- Return the slice itself, not its length and not its bounds.
- `run_case(case: dict)` forwards `case["stdin"]` to `solve`.
- Do not append a trailing newline to the returned string; return the value exactly once.