plugin: move match check to url setter, fix typing

[bastimeyer]

Raise PluginError when the url attr is set and it doesn't match any of the plugin's matchers, not just once upon class initialization.

Remove None type from Plugin.matcher and Plugin.match: Since the input URL must always match, it is pointless to annotate these attributes as potentially being None. This causes lots of headaches in plugin implementations because it requires type-narrowing. Initialize them with None, so plugin tests without matchers don't have to call hasattr().

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This fixes 120 typing errors in Streamlink's plugins, which are not checked by mypy by default, as this requires typing annotations (unless a custom config is set). ty checks this by default because of its Unknown type.

[bastimeyer]

These plugins update the url attribute dynamically:

$ git grep -nFE 'self.url = ' -- src/streamlink/plugins
src/streamlink/plugins/atresplayer.py:30:        self.url = update_scheme("https://", f"{self.url.rstrip('/')}/")
src/streamlink/plugins/bbciplayer.py:101:        self.url = urlunparse(urlparse(self.url)._replace(scheme="https"))
src/streamlink/plugins/dogan.py:108:            self.url = default_service_url
src/streamlink/plugins/filmon.py:189:            self.url = urlunparse(parsed._replace(path=parsed.path.replace("/channel/", "/tv/")))
src/streamlink/plugins/mangomolo.py:42:        self.url = update_scheme("https://", player_url)
src/streamlink/plugins/okru.py:70:        self.url = url
src/streamlink/plugins/oneplusone.py:68:        self.url = url
src/streamlink/plugins/steam.py:230:            self.url = self._watch_broadcast_url.format(steamid=steamid)
src/streamlink/plugins/streann.py:151:            self.url = iframes[0].attrib.get("src")
src/streamlink/plugins/twitcasting.py:180:        self.url = update_qsd(url, params or {})
src/streamlink/plugins/vk.py:62:            self.url = f"{parsed_url.scheme}://{parsed_url.netloc}/{true_path}"
src/streamlink/plugins/vk.py:69:            self.url = self.session.http.get(
src/streamlink/plugins/youtube.py:91:            self.url = urlunparse(parsed._replace(scheme="https", netloc="www.youtube.com"))
src/streamlink/plugins/youtube.py:93:            self.url = self._url_canonical.format(video_id=self.match["video_id"])
src/streamlink/plugins/youtube.py:95:            self.url = self._url_canonical.format(video_id=self.match["video_id"])
src/streamlink/plugins/youtube.py:97:            self.url = self._url_channelid_live.format(channel_id=self.match["live"])
src/streamlink/plugins/youtube.py:99:            self.url = urlunparse(parsed._replace(scheme="https"))
src/streamlink/plugins/youtube.py:379:            self.url = self._url_canonical.format(video_id=video_id)