Add offline workflow and coverage tests

pyproject.toml

@@ -19,8 +19,32 @@ backtrader = [
 
 [dependency-groups]
 dev = [
+    "coverage>=7.14.1",
     "pytest>=7.0.0",
 ]
 
 [tool.uv]
 package = false
+
+[tool.pytest.ini_options]
+markers = [
+    "network: tests that call live external data providers and are skipped unless explicitly enabled",
+]
+
+[tool.coverage.run]
+branch = true
+relative_files = true
+source = [
+    ".",
+]
+
+[tool.coverage.report]
+fail_under = 80
+show_missing = true
+skip_covered = false
+omit = [
+    "tests/*",
+    "docs/*",
+    "scripts/*",
+    ".venv/*",
+]