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-raid/src/raid/level_5.rs

@@ -136,7 +136,7 @@ impl RaidAlgorithm for Raid5 {
                 self.stripe_size - (current_offset % self.stripe_size),
             );
 
-            let chunk_data = &data[data_pos as usize..(data_pos + chunk_size as usize) as usize];
+            let chunk_data = &data[data_pos..(data_pos + chunk_size as usize) as usize];
 
             let old_data = self.read_from_member(data_disk, physical_offset, chunk_size)?;
             let old_parity = self.read_from_member(parity_disk, physical_offset, chunk_size)?;