macos: open URLs with NSWorkspace APIs instead of open

Fixes #5256

This updates the macOS apprt to implement the `OPEN_URL` apprt action to
use the NSWorkspace APIs instead of the `open` command line utility.

As part of this, we removed the `ghostty_config_open` libghostty API and
instead introduced a new `ghostty_config_open_path` API that returns the
path to open, and then we use the `NSWorkspace` APIs to open it (same
function as the `OPEN_URL` action).

macos/Sources/Ghostty/Package.swift

@@ -73,6 +73,26 @@ extension Ghostty {
 
 // MARK: Swift Types for C Types
 
+extension Ghostty {
+    class AllocatedString {
+        private let cString: ghostty_string_s
+        
+        init(_ c: ghostty_string_s) {
+            self.cString = c
+        }
+        
+        var string: String {
+            guard let ptr = cString.ptr else { return "" }
+            let data = Data(bytes: ptr, count: Int(cString.len))
+            return String(data: data, encoding: .utf8) ?? ""
+        }
+        
+        deinit {
+            ghostty_string_free(cString)
+        }
+    }
+}
+
 extension Ghostty {
     enum SetFloatWIndow {
         case on