selfhost: Integrate ChatGPT's using system parser fixes

- Fix using paths in mini_vm_prints.nyash and mini_vm_core.nyash
- Convert multi-line JSON literal to single-line in empty args smoke test
- Remove extra closing brace in mini_vm_core.nyash
- Add verbose logging for using system visited file tracking

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/runner/modes/common_util/resolve/strip.rs

@@ -166,7 +166,10 @@ pub fn strip_using_and_register(
                 }
                 if let Ok(abs) = std::fs::canonicalize(&p) { p = abs; }
                 let key = p.to_string_lossy().to_string();
-                if visited.contains(&key) { continue; }
+                if visited.contains(&key) { 
+                    if verbose { eprintln!("[using] skipping already visited: {}", key); }
+                    continue; 
+                }
                 visited.insert(key.clone());
                 if let Ok(text) = std::fs::read_to_string(&p) {
                     let inlined = strip_and_inline(runner, &text, &key, visited)?;