The usage example of 1-bit Quantized Arrays on the official website might be incorrect.

[Kakitan-saikou]

Describe the bug
The usage example of 1-bit Quantized Arrays on the official website(https://docs.taichi-lang.org/docs/quant) might be incorrect.

To Reproduce
Here's the usage example of 1-bit Quantized Arrays on the official website(https://docs.taichi-lang.org/docs/quant).
The quant arrays x and y should have been fields with 2 dims as shown in the official website, but actually it is 1 dim field.

import taichi as ti
ti.init(arch=ti.cpu)
u1 = ti.types.quant.int(1, False)
N = 512
M = 32
x = ti.field(dtype=u1)
y = ti.field(dtype=u1)
ti.root.dense(ti.i, N // M).quant_array(ti.i, M, max_num_bits=M).place(x)
ti.root.dense(ti.i, N // M).quant_array(ti.i, M, max_num_bits=M).place(y)

@ti.kernel
def assign_vectorized():
    ti.loop_config(bit_vectorize=True)
    for i, j in x:
        y[i, j] = x[i, j]  # 32 bits are handled at a time

assign_vectorized()

Log/Screenshots
[Taichi] mode=release
[Taichi] version 1.6.0, llvm 15.0.1, commit f1c6fbb, win, python 3.11.4
taichi.lang.exception.TaichiCompilationError:
File "D:--.py", line --, in assign_vectorized:
for i, j in x:
^^^^^^^^^^^^^^
Traceback (most recent call last):
File "C:\Users--\AppData\Roaming\Python\Python311\site-packages\taichi\lang\ast\ast_transformer_utils.py", line 27, in call
return method(ctx, node)
^^^^^^^^^^^^^^^^^
File "C:\Users--\AppData\Roaming\Python\Python311\site-packages\taichi\lang\ast\ast_transformer.py", line 1336, in build_For
return ASTTransformer.build_struct_for(ctx, node, is_grouped=False)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users--\AppData\Roaming\Python\Python311\site-packages\taichi\lang\ast\ast_transformer.py", line 1237, in build_struct_for
impl.begin_frontend_struct_for(ctx.ast_builder, expr_group, loop_var)
File "C:\Users--\AppData\Roaming\Python\Python311\site-packages\taichi\lang\impl.py", line 117, in begin_frontend_struct_for
raise IndexError(
IndexError: Number of struct-for indices does not match loop variable dimensionality (2 != 1). Maybe you wanted to use "for I in ti.grouped(x)" to group all indices into a single vector I?