feat(ir): give datatype some conveniences like `is_boolean`, `is_integer`, `is_int64`

[kszucs]

Let's make a follow-up issue to give datatype some Rust enum-like conveniences like is_boolean, is_integer, is_int64 etc.

Originally posted by @cpcloud in https://github.com/ibis-project/ibis/pull/4378#discussion_r953733703