feat: Add Test Case Generation for Weak Isolation Levels in Different Databases

[WeihuaSun]

issue #42 Generate different test cases for weak isolation levels of different databases.

The isolation level of the database has different capabilities to break the cycles in POP. If the isolation level can break the cycles in POP, then the test case corresponding to POP should not have data anomalies under the isolation level. I corresponded the isolation level with the ability to break the cycles and summarized 6 mechanisms.

By specifying the database and isolation level, the code can generate test cases for the isolation level.

[tencent-adm]

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