fix: macOS and Windows test/lint failures; repo.dixon.cx packaging for nexusterminal

CI hadn't run on macOS or Windows for a while (billing); once it did:
- Windows: the RDP shared-drive code and its symlink test are Unix-only
  but were compiled there (and the unused pieces failed clippy). The drive
  type, its impls, imports and test are now cfg(unix); refusing a drive
  request is a free function used everywhere. Other Windows-only warnings
  fixed (serial test import, unused mut, harden_process).
- macOS: the local shell's directory was sampled on the first output
  after Enter, which is the shell echoing the command before a cd runs,
  so restored tabs opened one directory behind. It's now sampled shortly
  after Enter and again once the command has had time to finish.
- packaging/repo.sh publishes the 'nexusterminal' .deb/.rpm/Arch packages
  to repo.dixon.cx from the release's own Linux binaries, verified
  against SHA256SUMS.
- The desktop entry mentions RDP.

rust/core/src/clients/rdp.rs

@@ -205,6 +205,7 @@ impl Client {
         }
         if self.cfg.shared_folder.is_some() || self.cfg.printer.is_some() {
             let mut devices = super::rdp_devices::Devices::default();
+            #[cfg_attr(not(unix), allow(unused_mut))]
             let mut drives = vec![];
             #[cfg(unix)]
             if let Some((folder, name)) = &self.cfg.shared_folder {