Refactoring relative markers

- get related issues in first pass and work with them
- unify before and after marker handling
- better handle combined ordinal and relative markers
- improves performance for relative marker handling

Author: mrbean-bremen

perf_tests/test_dependencies.py

@@ -42,4 +42,4 @@ def test_performance_dependency(fixture_path_relative):
     args = ["--order-dependencies", fixture_path_relative]
     TimedSorter.nr_marks = 400
     pytest.main(args, [pytest_order])
-    assert TimedSorter.elapsed < 0.4
+    assert TimedSorter.elapsed < 0.2

perf_tests/test_relative.py

@@ -41,4 +41,4 @@ def test_performance_relative(fixture_path_relative):
     args = [fixture_path_relative]
     TimedSorter.nr_marks = 400
     pytest.main(args, [pytest_order])
-    assert TimedSorter.elapsed < 0.5
+    assert TimedSorter.elapsed < 0.25

perf_tests/test_relative_dense.py

@@ -41,4 +41,4 @@ def test_performance_relative(fixture_path_relative_dense):
     args = [fixture_path_relative_dense]
     TimedSorter.nr_marks = 900
     pytest.main(args, [pytest_order])
-    assert TimedSorter.elapsed < 1.4
+    assert TimedSorter.elapsed < 0.25