Reconsider custom HTTP transport for package discovery #1851

PR #1849 preserves legacy package-discovery behavior for authenticated/private repositories, redirects, compressed responses, and repositories using ports blocked by the Fetch API.

It is unclear whether these cases are actively used or should remain part of vscode-R's long-term compatibility contract. Much of this behavior existed because it happened to work with the previous node-fetch implementation.

For vscode-R 4.0, reconsider whether we should keep the custom HTTP transport, or simplify package discovery to standard Fetch behavior and leave specialized repository access to R itself.