[1/x] fix: cargo-miden picks the correct package from cargo metadata

[greenhat]

Close #738

This PR removes using the root package in the cargo metadata to determine the package that we are compiling right now.

Now, we use only the following 2 methods:

1. Look for a package for which the manifest path points to the current directory;
2. What user provided in the --manifest-path option.

[greenhat]

@Keinberger I tested the fix on your workspace and it works. Try installing the cargo-miden from this branch.