fix: add warning log when Jest fails without XML output

When Jest fails early (e.g., due to import errors) and doesn't produce
XML output, the error was only logged at DEBUG level, making it hard
to diagnose issues.

This change adds WARNING level logging that includes Jest's stdout
and stderr when:
1. Jest exits with non-zero return code
2. No XML output file is created

This helps debug common issues like:
- Invalid import paths in generated tests
- Module resolution failures
- TypeScript compilation errors

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: misrasaurabh1

codeflash/languages/javascript/test_runner.py

@@ -313,6 +313,14 @@ def run_jest_behavioral_tests(
                 args=result.args, returncode=result.returncode, stdout=result.stdout + "\n" + result.stderr, stderr=""
             )
         logger.debug(f"Jest result: returncode={result.returncode}")
+        # Log Jest output at WARNING level if tests fail and no XML output will be created
+        # This helps debug issues like import errors that cause Jest to fail early
+        if result.returncode != 0 and not result_file_path.exists():
+            logger.warning(
+                f"Jest failed with returncode={result.returncode} and no XML output created.\n"
+                f"Jest stdout: {result.stdout[:2000] if result.stdout else '(empty)'}\n"
+                f"Jest stderr: {result.stderr[:500] if result.stderr else '(empty)'}"
+            )
     except subprocess.TimeoutExpired:
         logger.warning(f"Jest tests timed out after {timeout}s")
         result = subprocess.CompletedProcess(args=jest_cmd, returncode=-1, stdout="", stderr="Test execution timed out")