fix(hls): prefer media playlist keys over session keys for accurate KID matching

Session keys from master playlists often contain PSSHs with multiple KIDs covering all tracks, causing licensing to return keys for wrong KIDs.

Changes:
- Unified DRM licensing logic for all downloaders
- Prefer media playlist EXT-X-KEY tags which contain track-specific KIDs
- Add filter_keys_for_cdm() to select keys matching configured CDM type
- Add get_track_kid_from_init() to extract KID from init segment with fallback to drm.kid from PSSH
- Track initial_drm_key to prevent double-licensing on first segment
- Simplify n_m3u8dl_re block to reuse common licensing flow
- Use strict PlayReady keyformat matching via PR_PSSH.SYSTEM_ID URN instead of loose substring match
- Fix PlayReady keyformat comparisons that incorrectly compared strings to PlayReadyCdm class
- Fix byterange header format in get_track_kid_from_init() to use HLS.calculate_byte_range()

Also fixes PlayReady keyformat matching in:
- unshackle/core/tracks/track.py
- unshackle/core/drm/playready.py

Fixes download failures where track_kid was null or mismatched, causing wrong content keys to be obtained during PlayReady/Widevine licensing.

unshackle/core/tracks/track.py

@@ -215,7 +215,8 @@ class Track:
             # or when the subtitle has a direct file extension
             if self.downloader.__name__ == "n_m3u8dl_re" and (
                 self.descriptor == self.Descriptor.URL
-                or get_extension(self.url) in {
+                or get_extension(self.url)
+                in {
                     ".srt",
                     ".vtt",
                     ".ttml",
@@ -303,7 +304,9 @@ class Track:
                                 try:
                                     self.drm = [Widevine.from_track(self, session)]
                                 except Widevine.Exceptions.PSSHNotFound:
-                                    log.warning("No PlayReady or Widevine PSSH was found for this track, is it DRM free?")
+                                    log.warning(
+                                        "No PlayReady or Widevine PSSH was found for this track, is it DRM free?"
+                                    )
                         else:
                             try:
                                 self.drm = [Widevine.from_track(self, session)]
@@ -311,7 +314,9 @@ class Track:
                                 try:
                                     self.drm = [PlayReady.from_track(self, session)]
                                 except PlayReady.Exceptions.PSSHNotFound:
-                                    log.warning("No Widevine or PlayReady PSSH was found for this track, is it DRM free?")
+                                    log.warning(
+                                        "No Widevine or PlayReady PSSH was found for this track, is it DRM free?"
+                                    )
 
                     if self.drm:
                         track_kid = self.get_key_id(session=session)
@@ -548,7 +553,6 @@ class Track:
 
         try:
             import m3u8
-            from pyplayready.cdm import Cdm as PlayReadyCdm
             from pyplayready.system.pssh import PSSH as PR_PSSH
             from pywidevine.cdm import Cdm as WidevineCdm
             from pywidevine.pssh import PSSH as WV_PSSH
@@ -569,7 +573,7 @@ class Track:
                     pssh_b64 = key.uri.split(",")[-1]
                     drm = Widevine(pssh=WV_PSSH(pssh_b64))
                     drm_list.append(drm)
-                elif fmt == PlayReadyCdm or "com.microsoft.playready" in fmt:
+                elif fmt in {f"urn:uuid:{PR_PSSH.SYSTEM_ID}", "com.microsoft.playready"}:
                     pssh_b64 = key.uri.split(",")[-1]
                     drm = PlayReady(pssh=PR_PSSH(pssh_b64), pssh_b64=pssh_b64)
                     drm_list.append(drm)