Enhance V2EXService with caching configuration for improved network p…

…erformance

- Added a custom URLCache with 5MB memory and 20MB disk capacity to V2EXService.
- Configured URLSession to use the new cache and set request cache policy to return cached data if available, enhancing data retrieval efficiency.

V2Bar/Sources/Network/V2EXService.swift

@@ -7,10 +7,17 @@ actor V2EXService {
     private let session: Session
 
     private init() {
+        let cache = URLCache(
+            memoryCapacity: 5 * 1024 * 1024,      // 5MB 内存缓存
+            diskCapacity: 20 * 1024 * 1024        // 20MB 磁盘缓存
+        )
+
         let configuration = URLSessionConfiguration.default
         configuration.timeoutIntervalForRequest = 30
         configuration.timeoutIntervalForResource = 300
         configuration.waitsForConnectivity = true
+        configuration.urlCache = cache
+        configuration.requestCachePolicy = .returnCacheDataElseLoad
 
         session = Session(configuration: configuration)
     }