Fix code quality: trailing whitespace, unused imports, clippy warnings

- Fix trailing whitespace in kex.rs and s3.rs
- Add missing KexProposal import in kex_complete.rs
- Auto-fix clippy warnings across all crates
- All 153 tests pass

markbase-nfs/src/nfs/mod.rs

@@ -1,7 +1,7 @@
-pub mod markbase_fs;
 pub mod backend;
+pub mod markbase_fs;
 pub mod server;
 
-pub use markbase_fs::MarkBaseFS;
 pub use backend::MarkBaseNFSBackend;
-pub use server::{start_nfs_server, run_nfs_server};
+pub use markbase_fs::MarkBaseFS;
+pub use server::{run_nfs_server, start_nfs_server};