Refactor: drive discovery into platform files, no inline cfg

- drive/unix.rs: find_drives() + resolve_device() for Linux/macOS
- drive/windows.rs: find_drives() + resolve_device() + normalize_path() for Windows
- drive/mod.rs: clean delegation, no cfg branches
- scsi/windows.rs: SPTI transport only, no drive discovery

src/scsi/mod.rs

@@ -10,7 +10,7 @@ mod linux;
 #[cfg(target_os = "macos")]
 mod macos;
 #[cfg(target_os = "windows")]
-pub(crate) mod windows;
+mod windows;
 
 #[allow(unused_imports)]
 use crate::error::{Error, Result};