[Compatibility]: UUID() generates UUIDv7 instead of MySQL UUIDv1

### MatrixOne version

Latest `main` at `f72ca9efbeb3a7c673701e4a135cc6670c33cfde` (`VERSION()` reports `8.0.30-MatrixOne-v1.3.0`).

MySQL control: 8.3.0.

### What is different

MatrixOne's parameterless `UUID()` generates UUID version 7 values, while MySQL's parameterless `UUID()` generates UUID version 1 values.

This affects more than the textual UUID value. MySQL documents the two-argument `UUID_TO_BIN(uuid, 1)` optimization in terms of the version-1 layout produced by `UUID()`, so applications that use the MySQL `UUID()` + `UUID_TO_BIN(..., 1)` pattern receive a different UUID layout in MatrixOne.

### Reproduction

```sql
CREATE DATABASE uuid_compat;
USE uuid_compat;
CREATE TABLE t(seq INT PRIMARY KEY, u VARCHAR(36) NOT NULL);

INSERT INTO t VALUES
(1, UUID()), (2, UUID()), (3, UUID()), (4, UUID()),
(5, UUID()), (6, UUID()), (7, UUID()), (8, UUID());

SELECT SUBSTRING(u, 15, 1) AS version_nibble, COUNT(*) AS n
FROM t
GROUP BY SUBSTRING(u, 15, 1)
ORDER BY version_nibble;
```

MatrixOne returns:

```text
version_nibble | n
7 | 8
```

MySQL 8.3 returns:

```text
version_nibble | n
1 | 8
```

The comparison was repeated three times with 32 generated values per engine per run. MatrixOne produced 96/96 v7 values and MySQL produced 96/96 v1 values.

### Controls

MatrixOne's version-specific functions behave consistently, which isolates the difference to the parameterless `UUID()` mapping:

```sql
SELECT
UUID_EXTRACT_VERSION(UUID()),
UUID_EXTRACT_VERSION(UUID_V1()),
UUID_EXTRACT_VERSION(UUID_V7());
```

MatrixOne returns `7, 1, 7` in all three runs. `IS_UUID()`, `UUID_TO_BIN()`, and the matching `BIN_TO_UUID()` round trip also succeed for all generated values. The same `UUID()`/`UUID_V1()`/`UUID_V7()` version result is preserved through SQL `PREPARE`/`EXECUTE`.

### Why this is a compatibility issue

- [MySQL 8.4 reference](https://dev.mysql.com/doc/refman/8.4/en/miscellaneous-functions.html) states that `UUID()` returns UUID version 1, and that `UUID_TO_BIN(..., 1)` time-part swapping assumes version-1 values such as those generated by `UUID()`.
- [MatrixOne's current UUID documentation](https://github.com/matrixorigin/matrixorigin.io/blob/main/docs/MatrixOne/Reference/Functions-and-Operators/Other/uuid.md) declares `mysql_compat: full`, lists no MySQL differences, and also states that `UUID()` conforms to version 1.
- The implementation intentionally routes `UUID()` to v7: [`builtInUUID` calls `uuid.NewV7`](https://github.com/matrixorigin/matrixone/blob/f72ca9efbeb3a7c673701e4a135cc6670c33cfde/pkg/sql/plan/function/func_builtin.go#L1897-L1899), and the function registry describes `uuid_v7` as an alias of plain `uuid()` ([source](https://github.com/matrixorigin/matrixone/blob/f72ca9efbeb3a7c673701e4a135cc6670c33cfde/pkg/sql/plan/function/function_id.go#L807-L808)).

### Expected behavior

For MySQL compatibility, parameterless `UUID()` should retain MySQL's version-1 semantics, while `UUID_V7()` remains the explicit version-7 generator. If the v7 mapping is an intentional incompatible MatrixOne extension, it should be represented as an explicit compatibility difference rather than documented as full MySQL compatibility.