feat: An Initias Redis Store Implementation

- **docker-compose.yml**
  - Added Redis service configuration to support token storage.
  - Set up health checks and volume for Redis persistence.
  - Configured VRCAuthProxy service to depend on Redis.

- **HttpClientCookieContainer.cs**
  - Added `Username` property to support user-specific token management.

- **Program.cs**
  - Integrated Redis for storing and retrieving authentication tokens.
  - Updated login and token rotation logic to utilize Redis.
  - Improved async/await usage for better reliability.

- **VRCAuthProxy.csproj**
  - Added `StackExchange.Redis` package for Redis connectivity.
  - Corrected `Otp.NET` package reference.

- **API.cs**
  - Updated `TotpVerifyResponse` and `User` classes to be nullable-aware.

- **RedisService.cs**
  - Implemented Redis service for managing authentication tokens.
  - Added methods for saving, retrieving, and deleting tokens.

VRCAuthProxy/Services/RedisService.cs

@@ -0,0 +1,52 @@
+using System.Text.Json;
+using StackExchange.Redis;
+
+namespace VRCAuthProxy.Services;
+
+public class RedisService
+{
+    private readonly IConnectionMultiplexer _redis;
+    private readonly IDatabase _db;
+    private const string AUTH_TOKEN_KEY = "vrcauthproxy:tokens";
+
+    public RedisService(string connectionString)
+    {
+        _redis = ConnectionMultiplexer.Connect(connectionString);
+        _db = _redis.GetDatabase();
+    }
+
+    public async Task SaveAuthToken(string username, Dictionary<string, string> cookies)
+    {
+        var serializedCookies = JsonSerializer.Serialize(cookies);
+        await _db.HashSetAsync(AUTH_TOKEN_KEY, username, serializedCookies);
+    }
+
+    public async Task<Dictionary<string, string>?> GetAuthToken(string username)
+    {
+        var value = await _db.HashGetAsync(AUTH_TOKEN_KEY, username);
+        if (!value.HasValue) return null;
+        return JsonSerializer.Deserialize<Dictionary<string, string>>(value!);
+    }
+
+    public async Task<Dictionary<string, Dictionary<string, string>>> GetAllAuthTokens()
+    {
+        var entries = await _db.HashGetAllAsync(AUTH_TOKEN_KEY);
+        var result = new Dictionary<string, Dictionary<string, string>>();
+        
+        foreach (var entry in entries)
+        {
+            var cookies = JsonSerializer.Deserialize<Dictionary<string, string>>(entry.Value!);
+            if (cookies != null)
+            {
+                result[entry.Name!] = cookies;
+            }
+        }
+        
+        return result;
+    }
+
+    public async Task RemoveAuthToken(string username)
+    {
+        await _db.HashDeleteAsync(AUTH_TOKEN_KEY, username);
+    }
+}