Add pytest-cov

Author: msabramo

pyproject.toml

@@ -23,3 +23,8 @@ firefly = "firefly.cli:app"
 [build-system]
 requires = ["setuptools>=61.0"]
 build-backend = "setuptools.build_meta"
+
+[dependency-groups]
+dev = [
+    "pytest-cov>=6.1.1",
+]