Fix finding 30

[kunxian-xia]

Description

This PR added new constraints on tx table which enforce txs in a block are all included in the tx table.

Before this pr, it's possible to construct a tx table like this as we only asserts that tx_id <= block's cum_num_txs.

tx_id	block_num	cum_num_txs
1	1	1
2	2	2
3	5	7
4	5	7
5	5	7
6	5	7
7	0	0

and the block table is

block_num	num_txs	cum_num_txs
1	1	1
2	1	2
3	3	5
4	0	5
5	2	7

Note that this table is invalid in two ways:

1. txs (3 - 5) are included in the block 5 while they are actually are included in block 3.
2. The 2nd tx in block 5 is not included in the tx table.

To solve these bugs, we added one more field in the tx table prev_block_cnt which is current block's previous cumulative num of txs (it equals to cum_num_txs - num_txs). And we requires that

1. tx_id <= cum_num_txs and prev_block_cnt < tx_id: this will fix the 1st vulnerability;
2. last non-padding tx must have tx_id == cum_num_txs: this will fix the 2nd vulnerability.

Note that you cannot skip the very last tx in each block because if you do then it means tx_id < cum_num_txs. However, the next tx's tx_id' = tx_id + 1 and prev_block_cnt' = cum_num_txs. The above 1st constraint (prev_block_cnt' < tx_id') will just fail.

tx_id	block_num	cum_num_txs	prev_block_cnt
1	1	1	0
2	2	2	1
3	3	5	2
4	3	5	2
5	3	5	2
6	5	7	5
7	5	7	5

Issue Link

This PR aims to fix the finding 30 in the Zellic & Kalos Audit Report.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

[roynalnaruto]

Looks good to me!