Fuzzer testing for 2PC transactions

[GuptaManan100]

Description

This PR adds the fuzzer tests for the 2PC transactions.

The testing strategy involves running many transactions and checking that they all must be atomic.
To this end, we have a very unique strategy. We have two sharded tables twopc_fuzzer_update, and twopc_fuzzer_insert with the following columns.

• id: This is the sharding column. We use reverse_bits as the sharding vindex because it is easy to reason about where a row will end up.
• col in twopc_fuzzer_insert: An auto-increment column.
• col in twopc_fuzzer_update: This is a bigint value that we will use to increment on updates.
• updateSet: This column will store which update set the inserts where done for.
• threadId: It stores the thread id of the fuzzer thread that inserted the row.

The testing strategy is as follows -
Every transaction will do 2 things -

• One, it will increment the col on 1 row in each of the shards of the twopc_fuzzer_update table.
  To do this, we have sets of rows that each map to one shard. We prepopulate this before the test starts.
  These sets are stored in the fuzzer in updateRowsVals.
• Two, it will insert one row in each of the shards of the twopc_fuzzer_insert table and it will also store the update set that it updated the rows off.

We can check that a transaction was atomic by basically checking that the col value for all the rows that were updated together should match.
If any transaction was partially successful, then it would have missed an increment on one of the rows.
Moreover, the threadIDs of rows for a given update set in the 3 shards should be the same to ensure that conflicting transactions got committed in the same exact order.

Further Steps

The next steps are going to be to introduce thread level and cluster level disruptions to emulate failures that can happen during a real world system running, like PRS, a vttablet crashing, etc.

Related Issue(s)

• RFC: Atomic Distributed Transactions #16245

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• Tests were added or are not required
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• Documentation was added or is not required

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.62%. Comparing base (88d7033) to head (745a491).
Report is 4 commits behind head on main.

Additional details and impacted files

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- Coverage   68.63%   68.62%   -0.01%     
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  Files        1551     1551              
  Lines      199473   199515      +42     
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+ Hits       136906   136915       +9     
- Misses      62567    62600      +33     

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