API: Drive object, typed StreamUrl, tray lock/unlock, Send traits

- Rename DriveSession → Drive across entire codebase
- find_drives() returns Vec<Drive>, find_drive() returns Option<Drive>
- resolve_device() now pub(crate) — internal only
- StreamUrl is now a typed enum (Disc, Mkv, M2ts, Iso, Network, Stdio, Null)
  with scheme() and path_str() accessors, replacing struct of Strings
- Add lock_tray() / unlock_tray() for safe disc access during rips
- Improve reset() with eject cycle that clears LibreDrive stuck state
- Add Send bounds to ScsiTransport and PlatformDriver traits
- DiscOptions uses PathBuf instead of String for device/keydb paths
- Update doc example to use new Drive API

src/platform/mod.rs

@@ -5,7 +5,7 @@ pub mod mt1959;
 use crate::error::Result;
 use crate::scsi::ScsiTransport;
 
-pub(crate) trait PlatformDriver {
+pub(crate) trait PlatformDriver: Send {
     /// Unlock drive + upload firmware if needed.
     fn init(&mut self, scsi: &mut dyn ScsiTransport) -> Result<()>;