feat: Add stubs for soundfile and static_ffmpeg modules to facilitate testing

tests/__init__.py

@@ -0,0 +1,46 @@
+"""Test package initialization.
+
+Provides lightweight fallbacks for optional dependencies so unit tests can run
+without the full runtime stack.
+"""
+
+from __future__ import annotations
+
+import sys
+from types import ModuleType
+
+
+def _soundfile_write_stub(file_obj, data, samplerate, format="WAV", **_kwargs):  # pragma: no cover - stub
+    """Minimal stand-in for soundfile.write used in tests.
+
+    The real library streams waveform data to disk. Our tests don't exercise
+    audio synthesis, so it's safe to accept the call and write nothing.
+    """
+
+    if hasattr(file_obj, "write"):
+        try:
+            file_obj.write(b"")
+        except Exception:
+            # Ignore errors from exotic buffers; the real implementation would
+            # write binary samples, so a no-op keeps behavior predictable.
+            pass
+
+
+if "soundfile" not in sys.modules:  # pragma: no cover - import guard
+    stub = ModuleType("soundfile")
+    stub.write = _soundfile_write_stub  # type: ignore[attr-defined]
+    sys.modules["soundfile"] = stub
+
+
+def _static_ffmpeg_add_paths_stub(*_args, **_kwargs) -> None:  # pragma: no cover - stub
+    """Placeholder for static_ffmpeg.add_paths used in tests."""
+
+
+if "static_ffmpeg" not in sys.modules:  # pragma: no cover - import guard
+    ffmpeg_module = ModuleType("static_ffmpeg")
+    ffmpeg_module.add_paths = _static_ffmpeg_add_paths_stub  # type: ignore[attr-defined]
+    ffmpeg_run = ModuleType("static_ffmpeg.run")
+    ffmpeg_run.LOCK_FILE = ""  # type: ignore[attr-defined]
+    ffmpeg_module.run = ffmpeg_run  # type: ignore[attr-defined]
+    sys.modules["static_ffmpeg"] = ffmpeg_module
+    sys.modules["static_ffmpeg.run"] = ffmpeg_run