Support timestamp literals with precision specifier

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

Postgres supports an optional precision specifier in timestamp literals (e.g. `timestamp (3) '2021-01-01 00:00:00.123'` . The [postgres spec](https://www.postgresql.org/docs/current/datatype-datetime.html) technically only allows 0-6 but given that Arrow timestamps support nanoseconds it would probably be best to support 0-9.

### Describe the solution you'd like

For my purposes, It would be sufficient to only support precision values of 0, 3, 6, and 9 (seconds, milliseconds, microseconds, and nanoseconds) though it should be possible to support values that aren't a multiple of 3 since the expectation is that this value is only used for parsing the literal and it is not a constraint on the type at all (e.g. a timestamp(5) could be stored at microsecond resolution as long as the string is parsed correctly).

Ideally, output would look like the following:

```
❯ select arrow_typeof(timestamp (6) '2021-01-01 00:00:00.123456789');
+-------------------------------------------+
| arrow_typeof(Utf8("2021-01-01 00:00:00.123456")) |
+-------------------------------------------+
| Timestamp(Microsecond, None) |
+-------------------------------------------+

❯ select arrow_typeof(timestamp (3) '2021-01-01 00:00:00.123456789');
+-------------------------------------------+
| arrow_typeof(Utf8("2021-01-01 00:00:00.123")) |
+-------------------------------------------+
| Timestamp(Millisecond, None) |
+-------------------------------------------+

❯ select arrow_typeof(timestamp (0) '2021-01-01 00:00:00.123456789');
+-------------------------------------------+
| arrow_typeof(Utf8("2021-01-01 00:00:00")) |
+-------------------------------------------+
| Timestamp(Second, None) |
+-------------------------------------------+

❯ select arrow_typeof(timestamp (9) '2021-01-01 00:00:00.123456789');
+-------------------------------------------+
| arrow_typeof(Utf8("2021-01-01 00:00:00.123456789")) |
+-------------------------------------------+
| Timestamp(Nanosecond, None) |
+-------------------------------------------+
```

Example postgres output: https://www.db-fiddle.com/f/oiHdDy1v78mC1zKbCFvWdV/0

### Describe alternatives you've considered

A pretty usable workaround at the moment is to cast:

```
# These should be equivalent
timestamp (6) '2021-01-01 00:00:00'
arrow_cast(timestamp '2021-01-01 00:00:00', 'Timestamp(Microsecond, None)')
```

Unfortunately, this requires df-specific functions (arrow_cast) and it would also break backwards compatibility with Lance's current SQL parsing.

### Additional context

_No response_

Start by locating DataFusion's SQL parser entry point for timestamp literals and reviewing how Arrow timestamp precision is selected. Use the supplied arrow_typeof examples for precisions 0, 3, 6, and 9 as acceptance checks, including truncation of fractional seconds.

Written by the indexing model from the issue text.