refactor(analyzer): improve analyzer pipeline module (#1542)

* rename steps to pipeline module

* move pipeline entrypoint to pipeline module

* rename steps test module to pipeline

* fix paths after renames

* move step protocol to pipeline

* create pipeline status enum

* use Protocol from typing extensions

* Fix linting

analyzer/tests/pipeline/analyze_replaygain_test.py

@@ -0,0 +1,22 @@
+import distro
+import pytest
+
+from libretime_analyzer.pipeline.analyze_replaygain import analyze_replaygain
+
+from ..fixtures import FILES
+
+
+@pytest.mark.parametrize(
+    "filepath,replaygain",
+    map(lambda i: pytest.param(str(i.path), i.replaygain, id=i.path.name), FILES),
+)
+def test_analyze_replaygain(filepath, replaygain):
+    tolerance = 0.8
+
+    # On bionic, replaygain is a bit higher for loud mp3 files.
+    # This huge tolerance makes the test pass, with values devianting from ~-17 to ~-13
+    if distro.codename() == "bionic" and str(filepath).endswith("+12.mp3"):
+        tolerance = 5
+
+    metadata = analyze_replaygain(filepath, dict())
+    assert metadata["replay_gain"] == pytest.approx(replaygain, abs=tolerance)