[images]: convert save to use FilePath (#1574)

- Closes #1573.

Sources/ContainerCommands/Image/ImageSave.swift

@@ -23,6 +23,7 @@ import Containerization
 import ContainerizationError
 import ContainerizationOCI
 import Foundation
+import SystemPackage
 import TerminalProgress
 
 extension Application {
@@ -47,9 +48,13 @@ extension Application {
         @Option(
             name: .shortAndLong, help: "Pathname for the saved image", completion: .file(),
             transform: { str in
-                URL(fileURLWithPath: str, relativeTo: .currentDirectory()).absoluteURL.path(percentEncoded: false)
+                let path = FilePath(str)
+                guard path.isRelative else { return path.lexicallyNormalized() }
+                return FilePath(FileManager.default.currentDirectoryPath)
+                    .pushing(path)
+                    .lexicallyNormalized()
             })
-        var output: String?
+        var output: FilePath?
 
         @Option(
             help: "Platform for the saved image (format: os/arch[/variant], takes precedence over --os and --arch) [environment: CONTAINER_DEFAULT_PLATFORM]"
@@ -109,7 +114,9 @@ extension Application {
             }
 
             // Write to stdout; otherwise write to the output file
-            if output == nil {
+            if let output {
+                try await ClientImage.save(references: references, out: output.string, platform: p, containerSystemConfig: containerSystemConfig)
+            } else {
                 let tempFile = FileManager.default.temporaryDirectory.appendingPathComponent("\(UUID().uuidString).tar")
                 defer {
                     try? FileManager.default.removeItem(at: tempFile)
@@ -132,8 +139,6 @@ extension Application {
                     FileHandle.standardOutput.write(chunk)
                 }
                 try fileHandle.close()
-            } else {
-                try await ClientImage.save(references: references, out: output!, platform: p, containerSystemConfig: containerSystemConfig)
             }
 
             progress.finish()