feat(cdm): normalize CDM detection for local and remote implementations

Add unshackle.core.cdm.detect helpers to classify CDMs consistently across local and remote backends.

- Add is_playready_cdm/is_widevine_cdm for DRM selection across pyplayready, pywidevine, and wrappers

- Add is_remote_cdm/is_local_cdm/cdm_location so services can branch on CDM execution location

- Switch core DASH/HLS parsing, track DRM selection, and dl CDM switching away from brittle isinstance/DecryptLabs-only checks

- Make unshackle.core.cdm import-light via lazy __getattr__ so optional CDM deps are only imported when needed

unshackle/core/cdm/__init__.py

@@ -1,5 +1,57 @@
-from .custom_remote_cdm import CustomRemoteCDM
-from .decrypt_labs_remote_cdm import DecryptLabsRemoteCDM
-from .monalisa import MonaLisaCDM
+"""
+CDM helpers and implementations.
 
-__all__ = ["DecryptLabsRemoteCDM", "CustomRemoteCDM", "MonaLisaCDM"]
+Keep this module import-light: downstream code frequently imports helpers from
+`unshackle.core.cdm.detect`, which requires importing this package first.
+Some CDM implementations pull in optional/heavy dependencies, so we lazily
+import them via `__getattr__` (PEP 562).
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+__all__ = [
+    "DecryptLabsRemoteCDM",
+    "CustomRemoteCDM",
+    "MonaLisaCDM",
+    "is_remote_cdm",
+    "is_local_cdm",
+    "cdm_location",
+    "is_playready_cdm",
+    "is_widevine_cdm",
+]
+
+
+def __getattr__(name: str) -> Any:
+    if name == "DecryptLabsRemoteCDM":
+        from .decrypt_labs_remote_cdm import DecryptLabsRemoteCDM
+
+        return DecryptLabsRemoteCDM
+    if name == "CustomRemoteCDM":
+        from .custom_remote_cdm import CustomRemoteCDM
+
+        return CustomRemoteCDM
+    if name == "MonaLisaCDM":
+        from .monalisa import MonaLisaCDM
+
+        return MonaLisaCDM
+
+    if name in {
+        "is_remote_cdm",
+        "is_local_cdm",
+        "cdm_location",
+        "is_playready_cdm",
+        "is_widevine_cdm",
+    }:
+        from .detect import cdm_location, is_local_cdm, is_playready_cdm, is_remote_cdm, is_widevine_cdm
+
+        return {
+            "is_remote_cdm": is_remote_cdm,
+            "is_local_cdm": is_local_cdm,
+            "cdm_location": cdm_location,
+            "is_playready_cdm": is_playready_cdm,
+            "is_widevine_cdm": is_widevine_cdm,
+        }[name]
+
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")