Data type conversion issues

### Reference SQL
```
select name, avg(end_time - start_time)/1000.0 as duration, extract(minute from start_time) as minute
into minute_spans
from spans
group by name, extract(minute from start_time);

select name, avg(end_time-start_time)/1000.0 as duration, extract(hour from start_time) as hour
into hourly_spans
from spans
group by name, extract(hour from start_time);
```

- [x] #1185
- [ ] Subtraction between timestamps is returning i32. If my duration is in `nano` or `micro` seconds, information is lost.
- [x] #1184
- [ ] Timestamp to support nano and micro
- [ ] TypedService cannot convert Float types
- [ ] Can't `CAST` `float` to `int`
```
Invalid argument type for function CAST AS INT(): type: float, expected types: int, string, unsigned int, index: 0
```

Start by reproducing the reference SQL and the reported CAST error, then trace the timestamp subtraction and type-conversion paths in the repository. The issue names no files or tests, so first identify the relevant implementation and existing coverage; done means the listed timestamp precision and numeric conversion cases behave as expected.

Written by the indexing model from the issue text.