Some CBCS-encrypted content has an all-zeros default_KID in the tenc box while the real KID is only in the PSSH boxes. mp4decrypt matches keys against the tenc KID, so it silently skips decryption when the provided KID doesn't match. This adds a track ID-based key fallback when a zero KID is detected, matching the existing shaka-packager zero-KID fallback behavior.
* 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.
