fix(git): check destination emptiness without full readdir

Avoid reading an entire directory just to determine if clone destination is empty. Use ReadDir(1) to detect emptiness efficiently while preserving error behavior for non-empty and inaccessible paths.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: AdeshDeshmukh

pkg/lib/external/git/clone.go

@@ -19,6 +19,7 @@ package git
 import (
 	"errors"
 	"fmt"
+	"io"
 	"io/fs"
 	"os"
 	"os/exec"
@@ -113,13 +114,19 @@ func checkDestination(path string) error {
 	if !stat.IsDir() {
 		return fmt.Errorf("path %s exists and is not a directory", path)
 	}
-	// TODO: probably don't need to read the _whole_ directory
-	contents, err := os.ReadDir(path)
+	// Only check whether at least one entry exists; avoid reading full directory.
+	dir, err := os.Open(path)
 	if err != nil {
 		return fmt.Errorf("failed to inspect directory %s: %w", path, err)
 	}
-	if len(contents) > 0 {
+	defer dir.Close()
+
+	_, err = dir.ReadDir(1)
+	if err == nil {
 		return fmt.Errorf("cannot clone to a non-empty directory")
 	}
+	if !errors.Is(err, io.EOF) {
+		return fmt.Errorf("failed to inspect directory %s: %w", path, err)
+	}
 	return nil
 }