Adding makefile coverage

Makefile

@@ -8,6 +8,10 @@ help:     ## Show this help.
 tests: ## Run detailed tests
 	uv run pytest -v
 
+coverage: ## Run tests, and save coverage
+	uv run pytest --cov --cov-report=html:coverage
+	gio open coverage/index.html
+
 simple_tests: ## Run simple tests, without running SimStadt
 	uv run pytest -v -m "not live"
 
@@ -43,4 +47,4 @@ _upload:
 install_editable: ## Install package in dev mode
 	pip install -e .
 
-.PHONY: help tests simstadt build
+.PHONY: help tests simstadt build coverage