Inconsistent result for TO_SECONDS(numeric)

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```sql
CREATE TABLE t3342 (c1 NUMERIC);
INSERT t3342 () VALUES (950010);
INSERT t3342 () VALUES (12.991);
SELECT * FROM t3342 WHERE ((((TO_SECONDS(t3342.c1)) <= ALL (SELECT -3)) IS UNKNOWN));
-- 13
SELECT SUM(count) FROM (SELECT (((((TO_SECONDS(t3342.c1)) <= ALL (SELECT -3)) IS UNKNOWN))) IS TRUE AS count FROM t3342) AS ta_norec;
-- 2
```
### 2. What did you expect to see? (Required)
The SELECT * query should return both rows, and the SELECT SUM(count) query should return 2.
### 3. What did you see instead (Required)
The SELECT * query incorrectly returned only one row (13, which is the display format for 12.991).
The SELECT SUM(count) query returned 2.
### 4. What is your TiDB version? (Required)

Release Version: v8.5.0-20251010-ec6b882
Edition: Community
Git Commit Hash: https://github.com/pingcap/tidb/commit/ec6b882d188f77c199907ba26843a872b8c5fd6d
Git Branch: heads/refs/tags/v8.5.0-20251010-ec6b882
UTC Build Time: 2025-10-10 10:21:51
GoVersion: go1.23.3
Race Enabled: false
Check Table Before Drop: false
Store: unistore