fix: parse quoted charset values in content-type headers

`ResponseFactory.__extract_browser_encoding` matched the charset with
`charset=([\w-]+)`, which stops at a quote character. RFC 7231 permits the
charset value to be a quoted-string (e.g. `content-type: text/html;
charset="ISO-8859-1"`), so for any quoted charset the regex failed to match
and the function silently fell back to the `utf-8` default. A page served as
quoted ISO-8859-1 / windows-1252 / Shift_JIS would then be decoded as UTF-8,
producing mojibake.

Allow an optional surrounding quote in the pattern (`charset=["']?([\w-]+)`)
so the value is captured without the quote. Unquoted headers are unaffected.

The existing `content_type_map` fixture in tests/fetchers/test_utils.py was
unused; add focused tests covering unquoted, quoted, and missing charsets.

scrapling/engines/toolbelt/convertor.py

@@ -10,7 +10,7 @@ from scrapling.core.utils import log
 from .custom import Response, StatusText
 from scrapling.core._types import Dict, List, Optional
 
-__CHARSET_RE__ = re_compile(r"charset=([\w-]+)")
+__CHARSET_RE__ = re_compile(r"""charset=["']?([\w-]+)""")
 
 
 class ResponseFactory: