feat: hls content encoding support and shared session between different targets (#789)

* feat: key shared hls sessions by origin id
* feat: support hls content encoding
* fix: coderabbitai findings
* Fix: Custom headers are lost on provider://
In the manual redirect path, the abstract provider:// URL is compared against the resolved HTTP URL.
This causes the request to be marked as "scrubbed" before the first real redirect even occurs, stripping out headers like X-API-Key.

backend/src/processing/parser/m3u.rs

@@ -428,6 +428,7 @@ fn process_header_internal(
         }
     }
 
+    plih.freeze_input_stream_id();
     plih
 }