Support time precisions other than nanoseconds

[vrongmeal]

Description

We currently convert everything to nanos just because it’s easier (casting, comparision etc.) but this might cause some weird overflows when the datasource actually stores the value in some other precision.

We need to support other precision values.

See: https://github.com/GlareDB/glaredb/pull/2340#discussion_r1442901470

[tychoish]

One question that I think would be important to answer as part of this is, why--given that arrow supports different precisions for timestamps--doesn't this "just work" if we let datasources use their native types and let arrow's type system handle the appropriate conversions.