feat: don't crash LSP when there are errors resolving the workspace

[asterite]

Description

Problem

Before this PR, LSP would crash for assumed workspaces (when we can't find a Nargo.toml) or when there were errors in the Nargo.toml.

Summary

Now LSP doesn't crash in the above cases:

• for assumed workspaces we don't crash (we used to not crash but I made some changes in the past that broke this)
• for errors in Nargo.toml we now output to STDERR, so you can see the error in the output. This is what Rust Analyzer does, except that they also have a "rust-analyzer" thing at the bottom that becomes yellow when there's an error... I didn't implement this (it probably requires some code on the extension side) but I think if something doesn't work you'd check the logs or ask, and it's worse if it crashes.

Additional Context

Documentation

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[michaeljklein]

LGTM

Perhaps make a follow-up issue r.e. the following, in case someone doesn't see the logs in the STDERR and looks for an existing issue?

except that they also have a "rust-analyzer" thing at the bottom that becomes yellow when there's an error... I didn't implement this (it probably requires some code on the extension side) but I think if something doesn't work you'd check the logs or ask, and it's worse if it crashes.

[asterite]

Done! #6259