change `extract` return types to decimal to align with postgres

extract currently returns i32 which might loss some information

```bash
❯ select extract(second from timestamp '2000-01-01T00:00:00.1');
+--------------------------------------------------------+
| datepart(Utf8("SECOND"),Utf8("2000-01-01T00:00:00.1")) |
+--------------------------------------------------------+
| 0 |
+--------------------------------------------------------+
1 row in set. Query took 0.000 seconds.
```

while postgresql returns decimal

```bash
willy=# select extract(second from timestamp '2000-01-01T00:00:00.1');
extract
----------
0.100000
(1 row)
```

**Describe the solution you'd like**
A clear and concise description of what you want to happen.

change it to decimal

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
Add any other context or screenshots about the feature request here.

Start by locating the SQL EXTRACT implementation and reproduce the supplied SECOND-from-timestamp query, comparing its current result with the PostgreSQL example. Trace where the i32 return type is established and inspect existing coverage; done means fractional seconds are preserved and the relevant tests pass.

Written by the indexing model from the issue text.