Fix TRUNCATE operation not replicated to ClickHouse

[bakwc]

Description

This PR fixes the bug where TRUNCATE operations in MySQL were not being replicated to clear data on the ClickHouse side.

Fixes #155

Problem

When executing TRUNCATE TABLE in MySQL, the operation was detected in the binlog but not processed by the replication system. This resulted in:

• MySQL table being cleared ✅
• ClickHouse table retaining all data ❌
• Data inconsistency between MySQL and ClickHouse

Solution

Implementation

• Added TRUNCATE detection in DbReplicatorRealtime.handle_query_event()
• Implemented handle_truncate_query() method that:
  • Parses the table name from TRUNCATE queries
  • Clears any pending insert/delete operations for the affected table
  • Executes TRUNCATE TABLE on the corresponding ClickHouse table
• Added comprehensive test test_truncate_operation_bug_issue_155() to verify the fix

Changes Made

1. mysql_ch_replicator/db_replicator_realtime.py:

   • Added TRUNCATE query detection in handle_query_event()
   • Implemented handle_truncate_query() method with proper error handling
   • Added logging for TRUNCATE operations

2. test_mysql_ch_replicator.py:

   • Added reproduction test that initially fails (demonstrating the bug)
   • Test verifies both MySQL and ClickHouse are cleared after TRUNCATE
   • Test confirms replication continues to work after TRUNCATE operation

Testing

The test confirms:

• ✅ Before fix: Test fails with "ClickHouse table should be empty after TRUNCATE, but contains 3 records"
• ✅ After fix: Test passes - both MySQL and ClickHouse tables are properly cleared
• ✅ Replication continues: New records are properly replicated after TRUNCATE

# Test command
python3 -m pytest -v -s test_mysql_ch_replicator.py -k test_truncate_operation_bug_issue_155

Impact

• Resolves data consistency issues between MySQL and ClickHouse during TRUNCATE operations
• Maintains existing functionality - no breaking changes to other operations
• Follows established patterns in the codebase for query handling
• Comprehensive logging for troubleshooting TRUNCATE operations