Developer credentials (such as passwords, keys, and client IDs) are intended to be used by you and identify your API Client. You will keep your credentials confidential and make reasonable efforts to prevent and discourage other API Clients from using your credentials. Developer credentials may not be embedded in open source projects.
(https://developers.google.com/terms/, my emphasis)
Does this mean that my Open Source Drive command line client needs to force every user of my software to set up a new project in the Google Cloud console? Is there a better option?
It's not like it's hard to extract client ID and client "secret" from non-opensource, so why the distinction?
"Install applications" client IDs and secrets aren't really secrets, and Google documentation seems to agree:
The process results in a client ID and, in some cases, a client secret, which you embed in the source code of your application. (In this context, the client secret is obviously not treated as a secret.)
(https://developers.google.com/accounts/docs/OAuth2, again my emphasis)