Render image and video in galleries as a grid (#5929)

ElementX/Sources/Mocks/ContentScannerServiceMock.swift

@@ -11,15 +11,20 @@ struct ContentScannerServiceMockConfiguration {
     /// The verdict reported for every source: `true` when safe, `false` when unsafe, or `nil` to
     /// never resolve the scan so that the scanning state remains visible.
     var scanResult: Bool?
+    /// Overrides `scanResult` on a per-source basis, using the same `true`/`false`/`nil` semantics.
+    var perSourceScanResult: (@Sendable (MediaSourceProxy) -> Bool?)?
 }
 
 extension ContentScannerServiceMock {
     convenience init(_ configuration: ContentScannerServiceMockConfiguration) {
         self.init()
         
-        scanResultFromSourceReturnValue = configuration.scanResult
-        loadScanResultFromSourceClosure = { _ in
-            guard let scanResult = configuration.scanResult else {
+        let blanketScanResult = configuration.scanResult
+        let resolve: @Sendable (MediaSourceProxy) -> Bool? = configuration.perSourceScanResult ?? { _ in blanketScanResult }
+        
+        scanResultFromSourceClosure = { resolve($0) }
+        loadScanResultFromSourceClosure = { source in
+            guard let scanResult = resolve(source) else {
                 try? await Task.sleep(for: .seconds(3600))
                 return .failure(.failedScanning)
             }