[utils] Rework decoding of Content-Encodings

* support nested encodings
* support optional `br` encoding, if brotli package is installed
* support optional 'compress' encoding, if ncompress package is installed
* response `Content-Encoding` has only unprocessed encodings, or removed
* response `Content-Length` is decoded length (usable for filesize metadata)
* use zlib for both deflate and gzip decompression
* some elements taken from yt-dlp: thx especially coletdjnz

youtube_dl/compat.py

@@ -3200,6 +3200,18 @@ except AttributeError:
     def compat_datetime_timedelta_total_seconds(td):
         return (td.microseconds + (td.seconds + td.days * 24 * 3600) * 10**6) / 10**6
 
+# optional decompression packages
+# PyPi brotli package implements 'br' Content-Encoding
+try:
+    import brotli as compat_brotli
+except ImportError:
+    compat_brotli = None
+# PyPi ncompress package implements 'compress' Content-Encoding
+try:
+    import ncompress as compat_ncompress
+except ImportError:
+    compat_ncompress = None
+
 
 legacy = [
     'compat_HTMLParseError',
@@ -3234,6 +3246,7 @@ __all__ = [
     'compat_Struct',
     'compat_base64_b64decode',
     'compat_basestring',
+    'compat_brotli',
     'compat_casefold',
     'compat_chr',
     'compat_collections_abc',
@@ -3259,6 +3272,7 @@ __all__ = [
     'compat_itertools_zip_longest',
     'compat_kwargs',
     'compat_map',
+    'compat_ncompress',
     'compat_numeric_types',
     'compat_open',
     'compat_ord',