Unmount the auto-update disk image regardless of the auto-update status (#17019)

Closes #10782

In some cases, during the auto-update process,
the update can fail and leave a dangling disk image in macOS. If the
auto-update fails again, a new dangling mounted volume will be left
behind. To avoid polluting the system with these dangling mounted disk
images,
implement [the `Drop`
trait](https://doc.rust-lang.org/std/ops/trait.Drop.html) for the
`MacOSUnmounter` struct. This will ensure that the disk image
is unmounted when the `install_release_macos` function exits regardless
of its result.

## How to test this locally

Unfortunately, I was a bit too lazy to find a smarter way to test this,
so I simply commented out a bunch of lines to emulate the auto-update
process. To replicate the linked issue (#10782), you can apply the
attached patch. Build the Zed binary and run it. The auto-update should
fail, leaving the dangling mounted disk image in the system:

```shell
>diskutil list
/dev/disk5 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +220.6 MB   disk5
                                 Physical Store disk4s1
   1:                APFS Volume Zed                     190.6 MB   disk5s1
```

Run the Zed binary again to create another mounted disk image:

```shell
>diskutil list
/dev/disk5 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +220.6 MB   disk5
                                 Physical Store disk4s1
   1:                APFS Volume Zed                     190.6 MB   disk5s1

/dev/disk7 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +220.6 MB   disk7
                                 Physical Store disk6s1
   1:                APFS Volume Zed                     190.6 MB   disk7s1
```


[simulate_zed_autoupdate.patch](https://github.com/user-attachments/files/16787955/simulate_zed_autoupdate.patch)

Please let me know if the fix is good; otherwise, I am happy to
implement it differently. Thanks!

Release Notes:

- Fixed #10782

crates/auto_update/src/auto_update.rs

@@ -88,6 +88,34 @@ struct JsonRelease {
     url: String,
 }
 
+struct MacOsUnmounter {
+    mount_path: PathBuf,
+}
+
+impl Drop for MacOsUnmounter {
+    fn drop(&mut self) {
+        let unmount_output = std::process::Command::new("hdiutil")
+            .args(&["detach", "-force"])
+            .arg(&self.mount_path)
+            .output();
+
+        match unmount_output {
+            Ok(output) if output.status.success() => {
+                log::info!("Successfully unmounted the disk image");
+            }
+            Ok(output) => {
+                log::error!(
+                    "Failed to unmount disk image: {:?}",
+                    String::from_utf8_lossy(&output.stderr)
+                );
+            }
+            Err(error) => {
+                log::error!("Error while trying to unmount disk image: {:?}", error);
+            }
+        }
+    }
+}
+
 struct AutoUpdateSetting(bool);
 
 /// Whether or not to automatically check for updates.
@@ -739,6 +767,11 @@ async fn install_release_macos(
         String::from_utf8_lossy(&output.stderr)
     );
 
+    // Create an MacOsUnmounter that will be dropped (and thus unmount the disk) when this function exits
+    let _unmounter = MacOsUnmounter {
+        mount_path: mount_path.clone(),
+    };
+
     let output = Command::new("rsync")
         .args(&["-av", "--delete"])
         .arg(&mounted_app_path)
@@ -752,17 +785,5 @@ async fn install_release_macos(
         String::from_utf8_lossy(&output.stderr)
     );
 
-    let output = Command::new("hdiutil")
-        .args(&["detach"])
-        .arg(&mount_path)
-        .output()
-        .await?;
-
-    anyhow::ensure!(
-        output.status.success(),
-        "failed to unount: {:?}",
-        String::from_utf8_lossy(&output.stderr)
-    );
-
     Ok(running_app_path)
 }