docs(backend): add documentation to storage store types (#64)

Adds documentation to public storage store types (AccountStore, StorageStore, CodeStore) explaining their purpose, key/value semantics, and trait implementations.

Author: refcell

crates/storage/backend/src/accounts.rs

@@ -11,6 +11,13 @@ use crate::{
 };
 
 /// Account partition backed by commonware-storage.
+///
+/// Stores account state including nonce, balance, code hash, and generation number.
+/// Each account is keyed by its 20-byte address and encoded as a fixed 80-byte value
+/// using [`AccountEncoding`](kora_qmdb::AccountEncoding).
+///
+/// Implements [`QmdbGettable`] for reads and [`QmdbBatchable`] for batch writes.
+/// All writes are atomic and update the authenticated Merkle root.
 pub struct AccountStore {
     inner: StoreSlot<AccountDb>,
 }

crates/storage/backend/src/code.rs

@@ -11,6 +11,12 @@ use crate::{
 };
 
 /// Code partition backed by commonware-storage.
+///
+/// Stores contract bytecode keyed by the keccak256 hash of the code (code hash).
+/// Values are variable-length byte vectors containing the raw EVM bytecode.
+///
+/// Implements [`QmdbGettable`] for reads and [`QmdbBatchable`] for batch writes.
+/// All writes are atomic and update the authenticated Merkle root.
 pub struct CodeStore {
     inner: StoreSlot<CodeDb>,
 }

crates/storage/backend/src/storage.rs

@@ -13,6 +13,13 @@ use crate::{
 };
 
 /// Storage partition backed by commonware-storage.
+///
+/// Stores contract storage slots as key-value pairs. Keys are composite tuples of
+/// (address, generation, slot) encoded via [`StorageKey`], and values are 32-byte
+/// [`U256`] integers.
+///
+/// Implements [`QmdbGettable`] for reads and [`QmdbBatchable`] for batch writes.
+/// All writes are atomic and update the authenticated Merkle root.
 pub struct StorageStore {
     inner: StoreSlot<StorageDb>,
 }