Revise block tensor examples

[tran-go]

Revise block tensor examples

Summary

This PR revises the following block tensor examples:

• simple_block_matrix_broadcast.py
• simple_block_matrix_cumsum.py
• simple_block_matrix_vector_product.py

Changes

• Improve the example structure and readability.
• Update the examples to use the current block tensor API.
• Clarify the expected inputs and outputs.

Conclusion

The revised examples provide clearer demonstrations of block tensor broadcasting, cumulative sums, and matrix–vector multiplication.