fix(drm): handle non-UTF-8 output from shaka-packager stderr

Shaka-packager can emit non-UTF-8 bytes in its log output, causing UnicodeDecodeError when reading stderr in text mode. Use explicit errors="replace" encoding. Also harden try_ensure_utf8 fallback paths to always return valid UTF-8 instead of raw bytes.

unshackle/core/drm/playready.py

@@ -421,7 +421,9 @@ class PlayReady:
                 [binaries.ShakaPackager, *arguments],
                 stdout=subprocess.DEVNULL,
                 stderr=subprocess.PIPE,
-                universal_newlines=True,
+                text=True,
+                encoding="utf-8",
+                errors="replace",
             )
 
             stream_skipped = False

unshackle/core/utilities.py

@@ -516,10 +516,10 @@ def try_ensure_utf8(data: bytes) -> bytes:
                 # last ditch effort to detect encoding
                 detection_result = chardet.detect(data)
                 if not detection_result["encoding"]:
-                    return data
+                    return data.decode("utf-8", errors="replace").encode("utf-8")
-                return data.decode(detection_result["encoding"]).encode("utf8")
+                return data.decode(detection_result["encoding"], errors="replace").encode("utf8")
-            except UnicodeDecodeError:
+            except (UnicodeDecodeError, LookupError):
-                return data
+                return data.decode("utf-8", errors="replace").encode("utf-8")
 
 
 def get_free_port() -> int: