ci: move configuration to pyproject.toml and remove pytest.ini

Author: harryswift01

pyproject.toml

@@ -85,7 +85,17 @@ docs = [
 CodeEntropy = "CodeEntropy.cli:main"
 
 [tool.pytest.ini_options]
-addopts = "-n auto -m 'not slow' -vv"
+addopts = "-n auto -ra -vv --dist=loadscope"
+
+markers = [
+    "regression: end-to-end regression tests against baselines",
+    "slow: long-running regression tests (20-30+ minutes)"
+]
+
+testpaths = [
+    "tests/unit",
+    "tests/regression"
+]
 
 [tool.ruff]
 line-length = 88