feat(drm): ✨ Add support for mp4decrypt as a decryption method

* Introduced a new configuration option for DRM decryption in `unshackle.yaml`.
* Updated the `decrypt` methods in `PlayReady` and `Widevine` classes to allow using `mp4decrypt`.
* Enhanced the `Config` class to manage decryption methods per service.
* Added `mp4decrypt` binary detection in the binaries module.

unshackle/core/config.py

@@ -75,6 +75,14 @@ class Config:
         self.proxy_providers: dict = kwargs.get("proxy_providers") or {}
         self.serve: dict = kwargs.get("serve") or {}
         self.services: dict = kwargs.get("services") or {}
+        decryption_cfg = kwargs.get("decryption") or {}
+        if isinstance(decryption_cfg, dict):
+            self.decryption_map = {k.upper(): v for k, v in decryption_cfg.items()}
+            self.decryption = self.decryption_map.get("DEFAULT", "shaka")
+        else:
+            self.decryption_map = {}
+            self.decryption = decryption_cfg or "shaka"
+
         self.set_terminal_bg: bool = kwargs.get("set_terminal_bg", False)
         self.tag: str = kwargs.get("tag") or ""
         self.tmdb_api_key: str = kwargs.get("tmdb_api_key") or ""