Ensure `to_timestamp` behaves consistently with PostgreSQL

### Is your feature request related to a problem or challenge?

In postgres, `to_timestamp` has signature `to_timestamp ( text, text ) → timestamp with time zone` and `to_timestamp ( double precision ) → timestamp with time zone`.

But we have query that has more than 2 arguments

https://github.com/apache/datafusion/blob/7ebd993fe47e78006bad33256160716f73b13cef/datafusion/sqllogictest/test_files/timestamps.slt#L362-L366

Other than that the result seems different too.

Postgres
```
postgres=# select to_timestamp(1);
to_timestamp
---------------------------
1970-01-01 07:30:01+07:30
```

Duckdb
```
D select to_timestamp(1);
┌───────────────────────────┐
│ to_timestamp(1) │
│ timestamp with time zone │
├───────────────────────────┤
│ 1970-01-01 07:30:01+07:30 │
└───────────────────────────┘
```

Datafusion
```
query P
select to_timestamp(1);
----
1970-01-01T00:00:01
```

### Describe the solution you'd like

Change the function signature to be consistent with Postgres.
Change the result to be consistent with Postgres.

### Describe alternatives you've considered

_No response_

### Additional context

Duckdb doesn't support (text, text) signature

```
D select to_timestamp('05 Dec 2000', 'DD Mon YYYY');
Binder Error: No function matches the given name and argument types 'to_timestamp(STRING_LITERAL, STRING_LITERAL)'. You might need to add explicit type casts.
Candidate functions:
to_timestamp(DOUBLE) -> TIMESTAMP WITH TIME ZONE

LINE 1: select to_timestamp('05 Dec 2000', 'DD Mon YYY...
```

https://www.postgresql.org/docs/current/functions-formatting.html

Start with the timestamps.slt case linked at lines 362-366 and compare its current behavior with PostgreSQL's documented to_timestamp signatures and results. Trace the DataFusion implementation and update the overload behavior and timestamp result, then extend or adjust the timestamp SQL logic tests to verify both forms.

Written by the indexing model from the issue text.