This implementation heavily depends on there being a lockfile, meaning
JSR specifiers will always diagnose as uncached unless it's there. In
practice this affects cases where a `deno.json` isn't being used. Our
NPM specifier support isn't subject to this.
The reason for this is that the version constraint solving code is
currently buried in `deno_graph` and not usable from the LSP, so the
only way to reuse that logic is the solved-version map in the lockfile's
`packages.specifiers`.
