fix: Add numpy to dev dependencies for tests

Tests require numpy but it was missing from dev dependencies.
This resolves test failures in CI workflows.

Author: leebeanbin

pyproject.toml

@@ -59,6 +59,7 @@ dev = [
     "black>=23.0.0",
     "ruff>=0.1.0",
     "mypy>=1.0.0",
+    "numpy>=1.24.0",  # For tests
 ]
 
 [project.urls]