SELECT reports parsing error

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
```sql
CREATE TABLE t0(c0 CHAR UNIQUE );
CREATE TABLE t1(c0 TEXT(309) , c1 BOOL UNSIGNED );
INSERT IGNORE INTO t1 VALUES ('{ae', 607450541) ON DUPLICATE KEY UPDATE c0=',';

CREATE TABLE tt0(c0 char(1) COLLATE "utf8mb4_bin");
INSERT INTO tt0 SELECT * FROM t0;
CREATE TABLE tt1(c0 text COLLATE "utf8mb4_bin",c1 tinyint(1) unsigned);
INSERT INTO tt1 SELECT * FROM t1;

SELECT tt1.c0, tt1.c1, tt0.c0 FROM tt1, tt0 WHERE CAST(EXP(tt1.c1) AS DECIMAL);
```

### 2. What did you expect to see? (Required)

SELECT executed successfully

### 3. What did you see instead (Required)

```sql
ERROR 1105 (HY000): [components/tidb_query_datatype/src/codec/mysql/decimal.rs:1916]: parsing 556023164772767570000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 will overflow
```

### 4. What is your TiDB version? (Required)
·``sql
Release Version: v9.0.0-beta.1.pre-640-g24903d6b24
Edition: Community
Git Commit Hash: 24903d6b24674b9a43625ac2d05bf1b033b04407
Git Branch: master
UTC Build Time: 2025-04-27 01:17:32
GoVersion: go1.23.8
Race Enabled: false
Check Table Before Drop: false
Store: tikv
```

Start by running the supplied SQL reproduction on the reported TiDB version, then inspect components/tidb_query_datatype/src/codec/mysql/decimal.rs around line 1916. The work is done when this SELECT executes successfully without the decimal overflow parsing error, with coverage for the reproduction case.

Written by the indexing model from the issue text.