Exclude [workspace] from cunew-generated toml

[mik90]

I used cunew to generate a new project and hit a couple issues but this one is the one that makes most sense to fix.

I have a bit of an odd setup here. My user-side repo at $HOME/Repos/scratchpad and my Cargo workspace root is at $HOME/Repos/scratchpad/car. In my workspace, I just add all the crates in my project as members so I can build everything easily.

When I ran cunew, I ran it from the templates dir in my local copper repo, so this:

cd ~/Repos/copper-rs/templates
cargo cunew ~/Repos/scratchpad/car/copper
# Used 'git' as a copper source

When I built my code from the workspace root or the new copper project, I got this error

mike@fedora:copper $ cargo b
error: multiple workspace roots found in the same workspace:
  /home/mike/Repos/scratchpad/car/copper/car
  /home/mike/Repos/scratchpad/car

This is the reason this doesn't work: https://doc.rust-lang.org/cargo/reference/manifest.html#the-workspace-field

This field cannot be specified if the manifest already has a [workspace] table defined. That is, a crate cannot both be a root crate in a workspace (contain [workspace]) and also be a member crate of another workspace (contain package.workspace).

Omitting this element from the toml should fix it. I think that if users want this as the workspace root, they could add that in. I think this would relate to #142

Another issue I hit is that the local copper repo option only works if the generated project is in the copper repo. I hit a permission issue trying to refer to my copper repo from my new project, but I figure that might just be an intentional decision from cargo on how it manages directories/permissions anyways. Based on a skim of https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#specifying-path-dependencies, it doesn't seem like paths outside of repos are supported and I don't really blame them tbh.

Some conditional handling around new workspaces vs new projects in an existing workspace would make sense, but I think that having [workspace] in the toml makes the assumption that we're generating a new root workspace which isn't always true. Tell me if my understanding is wrong though.

[mik90]

So CI doesn't like this and it makes sense https://github.com/copper-project/copper-rs/actions/runs/12456810506/job/34770681064?pr=180

We could add templates/test-project to the root workspace and, even if it's not there, it works. However, I hate that. So maybe some jinja logic around the 'local' setting works because the 'local' setting implies that we're generating a new project in the existing copper workspace.

[gbin]

Thanks yes it makes sense to not create a workspace, this is just a quick starting point for the user anyway so we must accommodate the least opinionated option as possible