build: split pb and common to speed up compilation

[xxchan]

pb and common are the root of all other crates. Whenever they are modified, all crates need to re-compiled, which take a lot of time.

One example: We can try to make expr compile separately. It depends on very few stuff actually, not the whole pb and common crate.

• risingwave_pb::expr
• risingwave_common::{array,types,row,...}

Besides, these parts are modified rarely. If we separate these part out into new crates (maybe risingwave_pb_data and risingwave_data):

• They can be compile in an earlier stage, and compiled in parallel with the remaining crates. (In the image above, we can see risingwave_expr_impl started compilation after ~20s.)
• More importantly, they are less likely to be re-compiled due to unrelated changes.