Description

1. Support for ignoring binlog events that exceed chunk boundary values.
   If the value corresponding to the unique key of the binlog exceeds the maximum value of chunk iteration and is less than the maximum boundary value of the copy, it is ignored.

2. Support for binlog merge processing.
   When the columns of the unique key selected by chunk are int or float, the binlog is processed by map merging, and all delete operations are merged into one delete sql.All insert and update operations are merged into one replace sql. Then execute these sql in db transaction.

In case this PR introduced Go code changes:

• contributed code is using same conventions as original code
• script/cibuild returns with no formatting errors, build errors or unit test errors.

When there is only one column in a unique index, merging of DML binlog events is permitted.

…tionRangeMaxValues is nil

Add handling for the case when MigrationIterationRangeMaxValues is nil