Fix hjoin progress

[mdonaka]

Summary

Fix hjoin progress

Purpose

Check progress correctly with the progress bar

Contents

• Add comment
• Further split blocks for biased data

Let block_size=3, v1=[1, 2, 3, 4, 5], v2=[1, 4, 6, 7, 9].
The original implementation had block1=[[1,2,3],[4,5]], block2=[[1], [4,6,7,9]].
Since [4,6,7,9] in block2 exceeded block_size, progress also exceeded 100%.
Therefore, block2 is further divided.
After the change, it will be block1=[[1,2,3],[4,5],[4,5]], block2=[[1],[4,6,7],[9]].

Testing Methods Performed

• run hjoin for biased data with block_size set to 3
• CI