feature: more grace if top-level Cargo.toml DNE

[nick1udwig]

Is your feature request related to a problem? Please describe.
#227 errors out with a useful error message if process_lib's don't match within our project. However, it relies on the existence of a top-level Cargo.toml file and fails if that files does not exist.

Describe the solution you'd like
Warn if top-level Cargo.toml doesn't exist (since we can't do the check) and proceed without the check.

[nick1udwig]

Should think about how to make this nicer to use in general: https://discord.com/channels/1186394868336038080/1186684706700410962/1283942376288686111

Need to give users clear actions in errors AT A MINIMUM. Ideally we do the minimally invasive stopping of the bad error without harassing users in other cases.