feat(nadia): Implement power function in calculator.py

Outcome: done
Changed: src/calculator.py:12-13
Verified by: make verify — exit code 0, "verification passed"
Findings: power(base: int, exponent: int) -> int added to src/calculator.py:13 using the ** operator.
Open: none
Confidence: high - all five acceptance criteria satisfied

Typosaurus-Run: 57bb09b0f73f49dfab79b86f2b1bfc0d
Typosaurus-Node: 81dca8e4dae24ddeb48ee5eb9d68cc46
Typosaurus-Agent: @nadia
Refs: #4

src/calculator.py

@@ -6,3 +6,7 @@ def add(left: int, right: int) -> int:
 
 def subtract(left: int, right: int) -> int:
     return left - right
+
+
+def power(base: int, exponent: int) -> int:
+    return base ** exponent