Use .txt instead of .pdf for generated test files in upload example

The test file generator no longer produces PDF content, so naming them
.txt avoids confusion. Replaces fake PDF structure with plain repeating
text lines.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: tpellissier

examples/advanced/file_upload.py

@@ -90,32 +90,22 @@ def file_sha256(path: Path):  # returns (hex_digest, size_bytes)
 
 
 def generate_test_file(size_mb: int = 10) -> Path:
-    """Generate a dummy file of specified size for testing purposes.
+    """Generate a dummy text file of specified size for testing purposes.
 
-    Creates a minimal PDF-like file with random padding to reach the target
+    Creates a plain text file with repeating content to reach the target
     size. No external dependencies required.
     """
-    test_file = Path(__file__).resolve().parent / f"test_dummy_{size_mb}mb.pdf"
+    test_file = Path(__file__).resolve().parent / f"test_dummy_{size_mb}mb.txt"
     target_size = size_mb * 1024 * 1024
 
-    # Minimal PDF structure so the file is recognized as PDF
-    pdf_header = b"%PDF-1.4\n"
-    pdf_body = b"1 0 obj\n<< /Type /Catalog /Pages 2 0 R >>\nendobj\n"
-    pdf_body += b"2 0 obj\n<< /Type /Pages /Kids [3 0 R] /Count 1 >>\nendobj\n"
-    pdf_body += b"3 0 obj\n<< /Type /Page /Parent 2 0 R /MediaBox [0 0 612 792] >>\nendobj\n"
-
-    # Fill with dummy data to reach target size
-    current_size = len(pdf_header) + len(pdf_body)
-    padding_needed = target_size - current_size - 50  # Reserve space for trailer
-    padding = b"% " + (b"padding " * (padding_needed // 8))[:padding_needed] + b"\n"
-
-    pdf_trailer = b"xref\n0 4\ntrailer\n<< /Size 4 /Root 1 0 R >>\nstartxref\n0\n%%EOF\n"
-
+    line = b"The quick brown fox jumps over the lazy dog. " * 2 + b"\n"
     with test_file.open("wb") as f:
-        f.write(pdf_header)
-        f.write(pdf_body)
-        f.write(padding)
-        f.write(pdf_trailer)
+        written = 0
+        while written < target_size:
+            chunk = line * min(1000, (target_size - written) // len(line) + 1)
+            chunk = chunk[: target_size - written]
+            f.write(chunk)
+            written += len(chunk)
 
     print({"test_file_generated": str(test_file), "size_mb": test_file.stat().st_size / (1024 * 1024)})
     return test_file