reduce the number of dependencies pulled in by a few crates

[doy-materialize]

Motivation

• This PR refactors existing code.

in particular, this allows the cloud repository to share code without requiring it to pull in the full set of dependencies from the materialize repo.

Tips for reviewer

likely easier to review individual commits

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered.
  • this only changes code organization, not the functionality of the code, so as long as it still compiles, it should be fine.
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
  • this feels like a sufficiently small change
• This PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way) and therefore is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• This PR includes the following user-facing behavior changes:
  • no user facing changes