feat(docs): finish part 2

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm-starter/src/table/builder.rs

@@ -14,7 +14,7 @@ pub struct SsTableBuilder {
 }
 
 impl SsTableBuilder {
-    /// Create a builder based on target SST size and target block size.
+    /// Create a builder based on target block size.
     pub fn new(block_size: usize) -> Self {
         unimplemented!()
     }

mini-lsm-starter/src/table/iterator.rs

@@ -6,6 +6,7 @@ use std::sync::Arc;
 use anyhow::Result;
 
 use super::SsTable;
+use crate::iterators::impls::StorageIterator;
 
 /// An iterator over the contents of an SSTable.
 pub struct SsTableIterator {}
@@ -30,25 +31,22 @@ impl SsTableIterator {
     pub fn seek_to_key(&mut self, key: &[u8]) -> Result<()> {
         unimplemented!()
     }
+}
 
-    /// Get the current key.
-    pub fn key(&self) -> &[u8] {
+impl StorageIterator for SsTableIterator {
+    fn value(&self) -> &[u8] {
         unimplemented!()
     }
 
-    /// Get the current value.
-    pub fn value(&self) -> &[u8] {
+    fn key(&self) -> &[u8] {
         unimplemented!()
     }
 
-    /// Check if the iterator is valid.
-    pub fn is_valid(&self) -> bool {
+    fn is_valid(&self) -> bool {
         unimplemented!()
     }
 
-    /// Move to the next key-value pair.
-    #[allow(clippy::should_implement_trait)]
-    pub fn next(&mut self) -> Result<()> {
+    fn next(&mut self) -> Result<()> {
         unimplemented!()
     }
 }