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/surfsharkvpn.py

@@ -0,0 +1,124 @@
+import json
+import re
+import random
+from typing import Optional
+
+import requests
+
+from unshackle.core.proxies.proxy import Proxy
+
+
+class SurfsharkVPN(Proxy):
+    def __init__(self, username: str, password: str, server_map: Optional[dict[str, int]] = None):
+        """
+        Proxy Service using SurfsharkVPN Service Credentials.
+
+        A username and password must be provided. These are Service Credentials, not your Login Credentials.
+        The Service Credentials can be found here: https://my.surfshark.com/vpn/manual-setup/main/openvpn
+        """
+        if not username:
+            raise ValueError("No Username was provided to the SurfsharkVPN Proxy Service.")
+        if not password:
+            raise ValueError("No Password was provided to the SurfsharkVPN Proxy Service.")
+        if not re.match(r"^[a-z0-9]{48}$", username + password, re.IGNORECASE) or "@" in username:
+            raise ValueError(
+                "The Username and Password must be SurfsharkVPN Service Credentials, not your Login Credentials. "
+                "The Service Credentials can be found here: https://my.surfshark.com/vpn/manual-setup/main/openvpn"
+            )
+
+        if server_map is not None and not isinstance(server_map, dict):
+            raise TypeError(f"Expected server_map to be a dict mapping a region to a server ID, not '{server_map!r}'.")
+
+        self.username = username
+        self.password = password
+        self.server_map = server_map or {}
+
+        self.countries = self.get_countries()
+
+    def __repr__(self) -> str:
+        countries = len(set(x.get("country") for x in self.countries if x.get("country")))
+        servers = sum(1 for x in self.countries if x.get("connectionName"))
+
+        return f"{countries} Countr{['ies', 'y'][countries == 1]} ({servers} Server{['s', ''][servers == 1]})"
+
+    def get_proxy(self, query: str) -> Optional[str]:
+        """
+        Get an HTTP(SSL) proxy URI for a SurfsharkVPN server.
+        """
+        query = query.lower()
+        if re.match(r"^[a-z]{2}\d+$", query):
+            # country and surfsharkvpn server id, e.g., au-per, be-anr, us-bos
+            hostname = f"{query}.prod.surfshark.com"
+        else:
+            if query.isdigit():
+                # country id
+                country = self.get_country(by_id=int(query))
+            elif re.match(r"^[a-z]+$", query):
+                # country code
+                country = self.get_country(by_code=query)
+            else:
+                raise ValueError(f"The query provided is unsupported and unrecognized: {query}")
+            if not country:
+                # SurfsharkVPN doesnt have servers in this region
+                return
+
+            server_mapping = self.server_map.get(country["countryCode"].lower())
+            if server_mapping:
+                # country was set to a specific server ID in config
+                hostname = f"{country['code'].lower()}{server_mapping}.prod.surfshark.com"
+            else:
+                # get the random server ID
+                random_server = self.get_random_server(country["countryCode"])
+                if not random_server:
+                    raise ValueError(
+                        f"The SurfsharkVPN Country {query} currently has no random servers. "
+                        "Try again later. If the issue persists, double-check the query."
+                    )
+                hostname = random_server
+
+        return f"https://{self.username}:{self.password}@{hostname}:443"
+
+    def get_country(self, by_id: Optional[int] = None, by_code: Optional[str] = None) -> Optional[dict]:
+        """Search for a Country and it's metadata."""
+        if all(x is None for x in (by_id, by_code)):
+            raise ValueError("At least one search query must be made.")
+
+        for country in self.countries:
+            if all(
+                [
+                    by_id is None or country["id"] == int(by_id),
+                    by_code is None or country["countryCode"] == by_code.upper(),
+                ]
+            ):
+                return country
+
+    def get_random_server(self, country_id: str):
+        """
+        Get the list of random Server for a Country.
+
+        Note: There may not always be more than one recommended server.
+        """
+        country = [x["connectionName"] for x in self.countries if x["countryCode"].lower() == country_id.lower()]
+        try:
+            country = random.choice(country)
+            return country
+        except Exception:
+            raise ValueError("Could not get random countrycode from the countries list.")
+
+    @staticmethod
+    def get_countries() -> list[dict]:
+        """Get a list of available Countries and their metadata."""
+        res = requests.get(
+            url="https://api.surfshark.com/v3/server/clusters/all",
+            headers={
+                "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/128.0.0.0 Safari/537.36",
+                "Content-Type": "application/json",
+            },
+        )
+        if not res.ok:
+            raise ValueError(f"Failed to get a list of SurfsharkVPN countries [{res.status_code}]")
+
+        try:
+            return res.json()
+        except json.JSONDecodeError:
+            raise ValueError("Could not decode list of SurfsharkVPN countries, not JSON data.")