Fix Kate SQL Plugin PostgreSQL DDL Support and Multiple Statement Execution

Description

This PR fixes critical issues in the Kate SQL plugin's query execution engine that prevented proper PostgreSQL support and multiple statement execution.

Problem

The current SQL plugin has two major limitations:

PostgreSQL DDL Statement Failures: The plugin attempts to use prepared statements for ALL queries, including DDL statements (CREATE, ALTER, DROP) which PostgreSQL does not support in prepared statements, causing errors like:
```
ERROR: syntax error at or near "CREATE"
PREPARE qpsqlpstmt_2 AS CREATE TABLE voters;
```
Single Statement Limitation: The plugin can only execute one SQL statement per execution, making it impractical for running migration scripts or multiple related commands.

Solution

1. Smart Query Type Detection

Added DDL detection for statements starting with: CREATE, DROP, ALTER, TRUNCATE, COMMENT ON, GRANT, REVOKE, BEGIN, COMMIT, ROLLBACK
PostgreSQL-specific handling for additional statements: VACUUM, REINDEX, ANALYZE
Direct execution for non-preparable statements while maintaining prepared statement benefits for compatible queries

2. Multiple Statement Support

Advanced SQL parsing that properly handles:
- Semicolons within string literals
- Single-line (--) and multi-line (/* */) comments
- Parentheses in CREATE TABLE statements
Statement boundary detection that respects SQL syntax context

3. Enhanced Error Handling

Better error messages that include the problematic statement
Graceful fallback from prepared to direct execution when preparation fails
Proper result tracking across multiple statements

Key Changes

`sqlmanager.cpp`

Rewrote runQuery method with comprehensive SQL parsing
Added query classification logic to distinguish between DDL and DML
Implemented context-aware statement splitting
Enhanced PostgreSQL-specific optimizations

Testing

The fix has been validated with:

✅ PostgreSQL: CREATE TABLE, ALTER TABLE, DROP TABLE commands
✅ SQLite: Multiple statements in single execution
✅ Mixed scripts: DDL and DML statements in the same file
✅ Complex SQL: Statements with strings, comments, and parentheses

Backward Compatibility

Fully backward compatible with existing functionality
Maintains prepared statement benefits for compatible queries
No changes to public API or configuration interfaces

Benefits

PostgreSQL DDL Support: Users can now execute schema changes in PostgreSQL
Batch Execution: Multiple SQL statements can be executed in a single operation
Better User Experience: No more "Preparing the query failed" errors for valid SQL
Database Portability: Consistent behavior across different database systems

Example Usage

Before (would fail):

CREATE TABLE users (id SERIAL PRIMARY KEY, name VARCHAR(100));
INSERT INTO users (name) VALUES ('John Doe');
SELECT * FROM users;

After (executes successfully): All three statements execute in sequence within a single operation.

Related Issues

Fixes the long-standing limitation where users had to execute SQL statements one at a time and could not use DDL commands with PostgreSQL databases.

Checklist

Code follows Kate's coding conventions
PR description clearly describes problem and solution
Changes have been tested with multiple database systems
No regression in existing functionality
Documentation updated if applicable

This fix significantly enhances the Kate SQL plugin's usability for database development and administration tasks, making it a more robust tool for working with multiple database systems.

Fix: allow multiple SQL statements in sqlmanager plugin