Fix HTTPClient crash when download fails before shutdown (#837)

Currently, when `FileDownloader.downloadFile()` encounters an error
during `client.execute()` (e.g., XPC connection interruption or network
timeout), the `HTTPClient` instance is deallocated without calling
`shutdown()`, resulting in a crash:
`AsyncHTTPClient/HTTPClient.swift:187: Fatal error: Client not shut down
before the deinit.`

This caused to a control flow issue when attempting to download the
default kernel during `container system start` and, under certain
conditions (e.g., network latency), encountering the timeout error
`HTTPClientError.connectTimeout`.

To address this, `client.execute()` is now wrapped in a do/catch to
ensure `shutdown()` is always called on both success and error paths.
Also I've added an explicit timeout configuration (30s connect, no read
timeout) to better accommodate large file downloads.

Author: realrajaryan

Sources/ContainerClient/FileDownloader.swift

@@ -50,12 +50,23 @@ public struct FileDownloader {
             })
 
         let client = FileDownloader.createClient(url: url)
-        _ = try await client.execute(request: request, delegate: delegate).get()
+        do {
+            _ = try await client.execute(request: request, delegate: delegate).get()
+        } catch {
+            try? await client.shutdown()
+            throw error
+        }
         try await client.shutdown()
     }
 
     private static func createClient(url: URL) -> HTTPClient {
         var httpConfiguration = HTTPClient.Configuration()
+        // for large file downloads we keep a generous connect timeout, and
+        // no read timeout since download durations can vary
+        httpConfiguration.timeout = HTTPClient.Configuration.Timeout(
+            connect: .seconds(30),
+            read: .none
+        )
         if let host = url.host {
             let proxyURL = ProxyUtils.proxyFromEnvironment(scheme: url.scheme, host: host)
             if let proxyURL, let proxyHost = proxyURL.host {