Add integration test for batch warnings

Author: ggilder

localtests/panic-on-warnings-batch-middle/create.sql

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+drop table if exists gh_ost_test;
+create table gh_ost_test (
+  id int auto_increment,
+  email varchar(255) not null,
+  primary key (id)
+) auto_increment=1;
+
+-- Insert initial data - all unique emails
+insert into gh_ost_test (email) values ('[email protected]');
+insert into gh_ost_test (email) values ('[email protected]');
+insert into gh_ost_test (email) values ('[email protected]');
+
+-- Create an event that fires once, 2 seconds after creation
+-- By then gh-ost will have started and the binlog reader will be active
+-- The event generates 3 INSERTs that will be batched during binlog replay:
+-- 1. INSERT with duplicate PRIMARY KEY (id=1) - warning on migration key (filtered)
+-- 2. INSERT with duplicate email - warning on new unique index (should FAIL)
+-- 3. INSERT with valid data - would succeed if not for #2
+drop event if exists gh_ost_test;
+delimiter ;;
+create event gh_ost_test
+  on schedule at current_timestamp + interval 2 second
+  on completion not preserve
+  enable
+  do
+begin
+  -- This creates the critical test scenario:
+  -- Multiple DML events that will be batched together during binlog replay
+  insert ignore into gh_ost_test (id, email) values (1, '[email protected]'); -- ignored on primary db, gh-ost doesn't see
+  insert ignore into gh_ost_test (email) values ('[email protected]'); -- ok on primary db, should trigger warning on gh-ost due to duplicate email
+  insert ignore into gh_ost_test (email) values (concat('new', unix_timestamp(), '@example.com')); -- succeeds on both
+end ;;

localtests/panic-on-warnings-batch-middle/expect_failure

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+warnings detected in statement 1 of 2

localtests/panic-on-warnings-batch-middle/extra_args

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+--panic-on-warnings --alter "add unique index email_idx(email)"