Bitwise `&` and `->` group differently in the PostgreSQL and MySQL/Generic dialects

`&` and `->` have the same precedence in PostgreSQL but not in the default precedence table, so the
same expression produces two different trees depending on dialect:

| SQL | `PostgreSqlDialect` | `MySqlDialect` / `GenericDialect` |
|---|---|---|
| `a -> b & c` | `((a -> b) & c)` | `(a -> (b & c))` |
| `a -> b \| c` | `((a -> b) \| c)` | `((a -> b) \| c)` |
| `a -> b ^ c` | `(a -> (b ^ c))` | `(a -> (b ^ c))` |
| `a -> b + c` | `(a -> (b + c))` | `(a -> (b + c))` |

`&` is the only row that disagrees.

### Cause

The default table in `src/dialect/mod.rs` has:

```rust
Precedence::Ampersand => 23,
Precedence::Caret => 22,
Precedence::Pipe => 21,
Precedence::Colon => 21,
Precedence::PgOther => 21,
```

`PostgreSqlDialect::prec_value` instead maps `Ampersand`, `Pipe`, `Colon` and `PgOther` all to
`PG_OTHER_PREC` (`src/dialect/postgresql.rs:176-184`), which matches `gram.y`, where `&` is just a
generic `Op` and shares one left-associative level with `->`:

```
%left Op OPERATOR RIGHT_ARROW '|'
```

So `Pipe` already agrees with `PgOther` in the default table (both 21), and `Caret` is legitimately
above it, but `Ampersand` at 23 is left as the sole outlier.

### Candidate fix

```diff
- Precedence::Ampersand => 23,
+ Precedence::Ampersand => 21,
```

The full suite passes unchanged with that applied, so no existing test pins the current grouping —
which is also why this went unnoticed. `Display` for `Expr::BinaryOp` emits no parentheses, so a
mis-grouped tree round-trips to the original SQL and `verified_expr` / `verified_stmt` cannot catch
it; a test would have to assert on the tree.

### Open question, possibly a separate issue

For MySQL the fix above is necessary but not sufficient. MySQL's `->` / `->>` take a quoted JSON path
on the right-hand side, so there is nothing for MySQL to resolve — `col->'$.a' + 1` can only mean
`(col->'$.a') + 1`. sqlparser parses that right operand as a full expression at `PgOther`, giving
`col -> ('$.a' + 1)`, so `->` under-binds in MySQL against `+`, `*`, `^` and friends, not just `&`.
Making that correct probably means a MySQL-specific precedence for the arrow operators rather than
another adjustment to the shared row, so I've kept it out of scope here — happy to split it out if
a maintainer would prefer it tracked separately.

Surfaced while working on #2436. Related: #2460.

Bắt đầu trong src/dialect/mod.rs với bảng độ ưu tiên mặc định, sau đó so sánh nó với PostgreSqlDialect::prec_value trong src/dialect/postgresql.rs:176-184 và quy tắc PostgreSQL trong gram.y được trích dẫn trong issue. Thêm một bài kiểm thử hồi quy ở cấp cây cho `a -> b & c`, vì các bài kiểm thử round-trip SQL không thể phát hiện việc nhóm, rồi chạy toàn bộ bộ kiểm thử để xác minh thay đổi.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.