Keep private cache fixture source bytes consistent on Windows

Write explicit LF for filesystem source so checked-hash ZIP inputs match the same fixture bytes on every platform. Preserve all cache validity and foreign-format rejection assertions.

Assisted-by: OpenAI Codex:model identifier unavailable

extra_tests/snippets/private_315_cache_contract.py

@@ -18,7 +18,7 @@ if sys.implementation.name == "rustpython":
     with tempfile.TemporaryDirectory() as directory:
         root = Path(directory)
         source = root / "cache_subject.py"
-        source.write_text("value = 41\n", encoding="ascii")
+        source.write_text("value = 41\n", encoding="ascii", newline="\n")
         code = compile("value = 42\n", "byte_exact/cache_subject.py", "exec")
         stat = source.stat()
         headers = [
@@ -100,7 +100,7 @@ if sys.implementation.name == "rustpython":
                             raise AssertionError("foreign ZIP cache accepted")
 
         # Explicit py_compile writes under -B; all writers must use the private token.
-        source.write_text("value = 41\n", encoding="ascii")
+        source.write_text("value = 41\n", encoding="ascii", newline="\n")
         explicit = root / "explicit.pyc"
         previous = sys.dont_write_bytecode
         sys.dont_write_bytecode = True