support execute multi sql in ExecuteSQL

https://github.com/4paradigm/OpenMLDB/blob/06255ca9620adf0e0033411984081dab6906a79f/src/sdk/sql_cluster_router.cc#L2308

When we do `execute("sql1;sql2")`, only sql1 will be executed, and no warning about sql2.

We should support execute multi sql in `ExecuteSQL`

The issue points to sql_cluster_router.cc line 2308 where ExecuteSQL handles SQL strings. Start by examining that function to see how it parses and executes SQL. Look for existing parsing logic or splitting on semicolons. Check if there are tests for ExecuteSQL to understand the expected behavior. 'Done' means the function executes all statements in a semicolon-separated string and possibly returns warnings or errors for each.

Written by the indexing model from the issue text.