Fix [no_std] rust_analyzer error for cargo nexus new

[danielmarinq]

When creating a new Nexus project with cargo nexus new, rust analyzer shows the following error.

It should be fixable as described here: rust-lang/vscode-rust#729 (comment)

[govereau]

I don't think this is a complete fix for the issue. For instance, say I decide to add a new binary to my project by creating a file in src/bin. If I do this it will break again. Other sites suggest this is a configuration issue with VSCode: it assumes that all targets have a working std, which is not true, and the right way to fix it is to modify the VSCode configuration for the target. Of course, this is work each user has to do.

I can add the extra bits to Cargo.toml, but this is only a partial fix. Alternatively, I may be able to make a "fake" test crate in nexus_rt which will just hide the issue (not sure about this).

How do you think we should proceed?

[danielmarinq]

Yeah, I found this too while trying to fix it myself. Perhaps it's better to leave it for now. The fake test might be a good option, but this raises the question of how users will do tests inside their programs. E.g. tests would have to be run on the NVM as well.