ClickHouse: Parsing error for WITH statement using scalar expressions

### Describe the bug
The ClickHouseDialect parser fails to parse valid ClickHouse syntax when WITH clause is used declaring [scalar expressions](https://clickhouse.com/docs/sql-reference/statements/select/with#common-scalar-expressions).

### To Reproduce
```
use sqlparser::dialect::ClickHouseDialect;
use sqlparser::parser::Parser;

fn main() {
let sql = r#"
WITH 42 AS answer
SELECT answer FROM table
"#;

let dialect = ClickHouseDialect {};
let result = Parser::parse_sql(&dialect, sql);
println!("{:?}", result);
}
```
**Error:**
Err(ParserError("Expected: identifier, found: 42 at Line: 2, Column: 14"))

### Expected behavior tested in ClickHouse 26.1.2.11
The parser using ClickHouseDialect should accept the clause as ClickHouse does support it:
`WITH 42 AS answer SELECT answer FROM table`

### Additional context
The syntax from the [ClickHouse documentation](https://clickhouse.com/docs/sql-reference/statements/select/with#common-scalar-expressions-syntax) for this clause is: `WITH AS `
sqlparser version: 0.61

Start with ClickHouseDialect and reproduce the supplied Parser::parse_sql example for `WITH 42 AS answer SELECT answer FROM table`. Trace how the ClickHouse WITH clause is parsed, then verify that the parser accepts scalar expressions followed by an alias without regressing existing WITH handling.

由索引模型根据 Issue 内容生成。