Write a function grade_from_score(score: int) -> str that takes an integer score between 0 and 100 (inclusive) and returns the corresponding letter grade as a string. Use the following grading scale:
- 90 and above: "A"
- 80–89: "B"
- 70–79: "C"
- 60–69: "D"
- below 60: "F"
Hint: Make sure to use if/elif/else statements in the right order!