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/scsi/mod.rs

@@ -50,7 +50,7 @@ pub struct ScsiResult {
 }
 
 /// Low-level SCSI transport — one implementation per platform.
-pub trait ScsiTransport {
+pub trait ScsiTransport: Send {
     fn execute(
         &mut self,
         cdb: &[u8],