gh-133968: Add PyUnicodeWriter_WriteASCII() function (#133973)

Replace most PyUnicodeWriter_WriteUTF8() calls with
PyUnicodeWriter_WriteASCII().

Unrelated change to please the linter: remove an unused
import in test_ctypes.

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Objects/unicodeobject.c

@@ -14083,6 +14083,20 @@ _PyUnicodeWriter_WriteASCIIString(_PyUnicodeWriter *writer,
     return 0;
 }
 
+
+int
+PyUnicodeWriter_WriteASCII(PyUnicodeWriter *writer,
+                           const char *str,
+                           Py_ssize_t size)
+{
+    assert(writer != NULL);
+    _Py_AssertHoldsTstate();
+
+    _PyUnicodeWriter *priv_writer = (_PyUnicodeWriter*)writer;
+    return _PyUnicodeWriter_WriteASCIIString(priv_writer, str, size);
+}
+
+
 int
 PyUnicodeWriter_WriteUTF8(PyUnicodeWriter *writer,
                           const char *str,