feat(proxies): ✨ Add SurfsharkVPN support

Original code by @p0llux12 - Discord

- Introduced `SurfsharkVPN` class for proxy service integration.
- Updated configuration to include `surfsharkvpn` in proxy providers.
- Removed legacy `nordvpn` configuration from YAML.
- Enhanced `dl.py` and `search.py` to utilize `SurfsharkVPN`.

unshackle/core/config.py

@@ -71,7 +71,6 @@ class Config:
         self.headers: dict = kwargs.get("headers") or {}
         self.key_vaults: list[dict[str, Any]] = kwargs.get("key_vaults", [])
         self.muxing: dict = kwargs.get("muxing") or {}
-        self.nordvpn: dict = kwargs.get("nordvpn") or {}
         self.proxy_providers: dict = kwargs.get("proxy_providers") or {}
         self.serve: dict = kwargs.get("serve") or {}
         self.services: dict = kwargs.get("services") or {}