refactor: Simplify nonce management by replacing global cache with direct fetch

Remove NonceCache singleton pattern and replace with fetch_nonce_info function
that directly fetches nonce information from RPC. This simplifies the API by
eliminating cache initialization and state management, making it easier for
users to manage durable nonces.

docs/NONCE_CACHE.md

@@ -1,10 +1,10 @@
-# Nonce Cache Guide
+# Durable Nonce Guide
 
-This guide explains how to use Nonce Cache in Sol Trade SDK to implement transaction replay protection and optimize transaction processing.
+This guide explains how to use Durable Nonce in Sol Trade SDK to implement transaction replay protection and optimize transaction processing.
 
-## 📋 What is Nonce Cache?
+## 📋 What is Durable Nonce?
 
-Nonce Cache is a global singleton cache system for managing durable nonce accounts in the Solana network. Durable nonce is a Solana feature that allows you to create transactions that remain valid for extended periods, beyond the 150-block limitation of recent block hashes.
+Durable Nonce is a Solana feature that allows you to create transactions that remain valid for extended periods, beyond the 150-block limitation of recent block hashes.
 
 ## 🚀 Core Benefits
 
@@ -21,31 +21,23 @@ Nonce Cache is a global singleton cache system for managing durable nonce accoun
 You need to create a nonce account for your payer account first.
 Reference: https://solana.com/developers/guides/advanced/introduction-to-durable-nonces
 
-### 1. Initialize Nonce Cache
+### 1. Fetch Nonce Information
 
-First, set up the nonce account and initialize the cache:
+Directly fetch nonce information from RPC:
 
 ```rust
-use sol_trade_sdk::common::nonce_cache::NonceCache;
+use sol_trade_sdk::common::nonce_cache::fetch_nonce_info;
+use solana_sdk::pubkey::Pubkey;
+use std::str::FromStr;
 
 // Set up nonce account
-let nonce_account_str = "your_nonce_account_address_here";
-NonceCache::get_instance().init(Some(nonce_account_str.to_string()));
+let nonce_account = Pubkey::from_str("your_nonce_account_address_here")?;
+
+// Fetch nonce information
+let durable_nonce = fetch_nonce_info(&client.rpc, nonce_account).await;
 ```
 
-### 2. Fetch Nonce Information
-
-Get the latest nonce information from RPC:
-
-```rust
-// Fetch and update nonce information
-NonceCache::get_instance().fetch_nonce_info_use_rpc(&client.rpc).await?;
-// Or manually manage nonce
-// NonceCache::get_instance().update_nonce_info_partial(nonce_account, current_nonce, used);
-let durable_nonce = NonceCache::get_durable_nonce_info();
-```
-
-### 3. Use Nonce in Transactions
+### 2. Use Nonce in Transactions
 
 Set nonce parameters: durable_nonce
 
@@ -63,20 +55,19 @@ let buy_params = sol_trade_sdk::TradeBuyParams {
     close_wsol_ata: false,
     create_mint_ata: true,
     open_seed_optimize: false,
-    durable_nonce: Some(durable_nonce), // Set durable nonce
+    durable_nonce: durable_nonce, // Set durable nonce
 };
 
 // Execute transaction
 client.buy(buy_params).await?;
 ```
 
-## 🔄 Nonce Lifecycle
+## 🔄 Nonce Usage Flow
 
-1. **Initialize**: Set nonce account address
-2. **Fetch**: Get the latest nonce value from RPC
-3. **Use**: Set nonce parameters in transactions
-4. **Refresh**: Fetch new nonce value before next use
+1. **Fetch**: Get the latest nonce value from RPC
+2. **Use**: Set nonce parameters in transactions
+3. **Refresh**: Call `fetch_nonce_info` again before next use to get new nonce value
 
 ## 🔗 Related Documentation
 
-- [Example: Nonce Cache](../examples/nonce_cache/)
+- [Example: Durable Nonce](../examples/nonce_cache/)