[Bug]: show snapshots / show pitr column names changed case between main and 3.0-dev branches

### Is there an existing issue for the same bug?

- [x] I have checked the existing issues.

### Branch Name

main

### Commit ID

21a86006f838e9401ff046449c91ebcb5e0d7001

### Other Environment Information

```Markdown
- Hardware parameters:
- OS type:
- Others:
```

### Actual Behavior

## Problem Description

The column names returned by `SHOW SNAPSHOTS` and `SHOW PITR` commands have different cases between `main` and `3.0-dev` branches, causing compatibility issues and test failures.

## Branch Comparison

### `main` branch (uppercase)
```sql
SHOW SNAPSHOTS;
-- Returns:
-- SNAPSHOT_NAME TIMESTAMP SNAPSHOT_LEVEL ACCOUNT_NAME DATABASE_NAME TABLE_NAME

SHOW PITR;
-- Returns:
-- PITR_NAME CREATED_TIME MODIFIED_TIME PITR_LEVEL ACCOUNT_NAME DATABASE_NAME TABLE_NAME PITR_LENGTH PITR_UNIT

3.0-dev branch (lowercase)
SHOW SNAPSHOTS;
-- Returns:
-- snapshot_name timestamp snapshot_level account_name database_name table_name

SHOW PITR;
-- Returns:
-- pitr_name created_time modified_time pitr_level account_name database_name table_name pitr_length pitr_unit

### Expected Behavior

_No response_

### Steps to Reproduce

```Markdown
SHOW SNAPSHOTS;
SHOW PITR;
```

### Additional information

_No response_