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/proxies/__init__.py

@@ -1,5 +1,6 @@
 from .basic import Basic
 from .hola import Hola
 from .nordvpn import NordVPN
+from .surfsharkvpn import SurfsharkVPN
 
-__all__ = ("Basic", "Hola", "NordVPN")
+__all__ = ("Basic", "Hola", "NordVPN", "SurfsharkVPN")