Feature Not Supported: EXPLAIN PARTITIONS Syntax Not Supported

# Issue: EXPLAIN PARTITIONS Syntax Not Supported

## Description

MatrixOne does not support the `EXPLAIN PARTITIONS` syntax for viewing which partitions are accessed by a query. This is a standard MySQL feature for partition-aware query analysis.

## Error Statement

```sql
EXPLAIN PARTITIONS SELECT * FROM test_partition_range WHERE created_date = '2022-06-15';
```

## Error Message

```
ERROR 1064 (HY000) at line 1: SQL parser error: You have an error in your SQL syntax; check the manual that corresponds to your MatrixOne server version for the right syntax to use. syntax error at line 1 column 25 near " SELECT * FROM test_partition_range WHERE created_date = '2022-06-15'"
```

## Expected Behavior

The statement should display the query execution plan along with information about which partitions are accessed (partition pruning information).

## Actual Behavior

MatrixOne reports a syntax error, indicating that the `EXPLAIN PARTITIONS` syntax is not recognized by the parser.

## Impact

- Users cannot analyze partition pruning in query execution plans
- Must use regular EXPLAIN which doesn't show partition information
- Limits query optimization and debugging capabilities
- Migration from MySQL may require different query analysis approaches

## Test Case

**Case ID**: 612
**Test File**: `test_batch_62_partition.sql`
**Test Type**: Partition - EXPLAIN PARTITIONS command

## Related Information

- MatrixOne supports regular EXPLAIN for query plans
- Other partition query features (SHOW PARTITIONS, PARTITION() syntax) are also not supported
- This is part of comprehensive partition functionality testing