…than day (apache#49429)

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

should consider the microseconds' effect.

before:
```sql
mysql> select hours_diff('2023-10-15 00:00:00', '2023-10-14 00:00:00.1');
+------------------------------------------------------------+
| hours_diff('2023-10-15 00:00:00', '2023-10-14 00:00:00.1') |
+------------------------------------------------------------+
|                                                         24 |
+------------------------------------------------------------+
```
now:
```sql
mysql> select hours_diff('2023-10-15 00:00:00', '2023-10-14 00:00:00.1');
+------------------------------------------------------------+
| hours_diff('2023-10-15 00:00:00', '2023-10-14 00:00:00.1') |
+------------------------------------------------------------+
|                                                         23 |
+------------------------------------------------------------+
```

fix the wrong floor of function date_diff when unit less than day

- Test <!-- At least one of them must be included. -->
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    - [ ] Unit Test
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    - [ ] No need to test or manual test. Explain why:
- [ ] This is a refactor/code format and no logic has been changed.
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- Behavior changed:
    - [x] No.
    - [ ] Yes. <!-- Explain the behavior change -->

- Does this need documentation?
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- [ ] Yes. <!-- Add document PR link here. eg:
apache/doris-website#1214 -->

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