add function to combine accumulator update

[cctdaniel]

add function to combine accumulator updates by:

1. iterate through the list of update_data and check their vaa
2. for those with the same vaa, combine them into one accumulator update by incrementing the number of updates in the first update_data and appending the update to updates
3. for those with different vaa, keep them
4. serialize them back to the accumulator update_data format

[cctdaniel]

this name is based on the Accumulator Wire Format document on Notion

[ali-behjati]

It is very nice! i think there are some duplicate codes that we can remove. I like to review again after you removed them.

[ali-behjati]

Very nice!