fix: Restore sha256Hash extension for ImageCache

The sha256Hash() extension was accidentally removed when deleting
Data+InviteCrypto.swift, but ImageCache depends on it.

Author: yewreeka

ConvosCore/Sources/ConvosCore/Shared/Data+Crypto.swift

@@ -0,0 +1,10 @@
+import CryptoKit
+import Foundation
+
+extension Data {
+    /// Computes SHA256 hash of this data
+    func sha256Hash() -> Data {
+        let hash = SHA256.hash(data: self)
+        return Data(hash)
+    }
+}