feat: add gas fee strategy system with examples

- Add GasFeeStrategy module supporting normal and high-low fee strategies
- Initialize gas fee strategies in all examples
- Update documentation and README with gas fee strategy configuration
- Improve nonce cache documentation emphasizing latest nonce usage
- Adjust default gas fee configuration parameters
- Remove duplicate imports and unused constant references

docs/GAS_FEE_STRATEGY.md

@@ -0,0 +1,65 @@
+# 📊 Gas Fee Strategy Guide
+
+This document introduces the Gas Fee strategy configuration and usage methods in Sol Trade SDK.
+
+## Basic Usage
+
+### 1. Overview
+
+This module supports users to configure strategies for SwqosType under different TradeType (buy/sell).
+
+- Normal strategy: One SwqosType sends one transaction, specifying cu_limit, cu_price, and tip.
+- High-low fee strategy: One SwqosType sends two transactions simultaneously, one with low tip and high priority fee, another with high tip and low priority fee.
+
+Each (SwqosType, TradeType) combination can only configure one strategy. Subsequent strategy configurations will override previous ones.
+
+### 2. Using Built-in Strategies
+
+```rust
+use sol_trade_sdk::common::gas_fee_strategy::GasFeeStrategy;
+// Use built-in strategies (includes normal strategies for various SwqosTypes)
+GasFeeStrategy::init_builtin_fee_strategies();
+```
+
+### 3. Configuring Single Strategy
+
+```rust
+// Configure normal strategy for SwqosType::Jito during Buy
+GasFeeStrategy::add_normal_fee_strategy(
+    SwqosType::Jito,
+    TradeType::Buy,
+    xxxxx, // cu_limit
+    xxxx,  // cu_price
+    xxxxx  // tip
+);
+```
+
+### 4. Configuring High-Low Fee Strategy
+
+```rust
+// Configure high-low fee strategy for SwqosType::Jito during Buy
+GasFeeStrategy::add_high_low_fee_strategy(
+    SwqosType::Jito,
+    TradeType::Buy,
+    xxxxx, // cu_limit
+    xxxxx, // low cu_price
+    xxxxx, // high cu_price
+    xxxxx, // low tip
+    xxxxx  // high tip
+);
+```
+
+### 5. Viewing and Cleanup
+
+```rust
+// Remove a specific strategy
+GasFeeStrategy::remove_strategy(SwqosType::Jito, TradeType::Buy);
+// View all strategies
+GasFeeStrategy::print_all_strategies();
+// Clear all strategies
+GasFeeStrategy::clear();
+```
+
+## 🔗 Related Documents
+
+- [Example: Gas Fee Strategy](../examples/gas_fee_strategy/)

docs/GAS_FEE_STRATEGY_CN.md

@@ -0,0 +1,65 @@
+# 📊 Gas Fee 策略指南
+
+本文档介绍 Sol Trade SDK 中的 Gas Fee 策略配置和使用方法。
+
+## 基础使用
+
+### 1. 说明
+
+该模块支持用户配置 SwqosType 在不同 TradeType(buy/sell) 下的策略。
+
+- normal 策略: 一个 SwqosType 发送一笔交易，指定 cu_limit、cu_price 和小费。
+- 高低费率策略: 一个 SwqosType 同时发送两笔交易，一笔低小费高优先费，一笔高小费低优先费。
+
+每个 (SwqosType, TradeType) 的组合仅可配置一个策略。后续配置的策略会覆盖之前的策略。
+
+### 2. 使用内置策略
+
+```rust
+use sol_trade_sdk::common::gas_fee_strategy::GasFeeStrategy;
+// 使用内置策略（内置了各个 SwqosType 的 normal 策略）
+GasFeeStrategy::init_builtin_fee_strategies();
+```
+
+### 3. 配置单个策略
+
+```rust
+// 为 SwqosType::Jito 在 Buy 时配置 normal 策略
+GasFeeStrategy::add_normal_fee_strategy(
+    SwqosType::Jito,
+    TradeType::Buy,
+    xxxxx, // cu_limit
+    xxxx,  // cu_price
+    xxxxx  // tip
+);
+```
+
+### 4. 配置高低费率策略
+
+```rust
+// 为 SwqosType::Jito 在 Buy 时配置高低费率策略
+GasFeeStrategy::add_high_low_fee_strategy(
+    SwqosType::Jito,
+    TradeType::Buy,
+    xxxxx, // cu_limit
+    xxxxx, // low cu_price
+    xxxxx, // high cu_price
+    xxxxx, // low tip
+    xxxxx  // high tip
+);
+```
+
+### 5. 查看和清理
+
+```rust
+// 移除某个策略
+GasFeeStrategy::remove_strategy(SwqosType::Jito, TradeType::Buy);
+// 查看所有策略
+GasFeeStrategy::print_all_strategies();
+// 清空所有策略
+GasFeeStrategy::clear();
+```
+
+## 🔗 相关文档
+
+- [示例：Gas Fee 策略](../examples/gas_fee_strategy/)

docs/NONCE_CACHE.md

@@ -57,7 +57,7 @@ let buy_params = sol_trade_sdk::TradeBuyParams {
     mint: mint_pubkey,
     sol_amount: buy_sol_amount,
     slippage_basis_points: Some(100),
-    recent_blockhash: current_nonce, // Use nonce as blockhash
+    recent_blockhash: current_nonce, // Use nonce as blockhash. Please use the latest nonce value for each transaction.
     extension_params: Box::new(PumpFunParams::from_trade(&trade_info, None)),
     lookup_table_key: None,
     wait_transaction_confirmed: true,

docs/NONCE_CACHE_CN.md

@@ -57,7 +57,7 @@ let buy_params = sol_trade_sdk::TradeBuyParams {
     mint: mint_pubkey,
     sol_amount: buy_sol_amount,
     slippage_basis_points: Some(100),
-    recent_blockhash: current_nonce, // 使用 nonce 作为 blockhash
+    recent_blockhash: current_nonce, // 使用 nonce 作为 blockhash。请在每次交易时，都使用最新的 nonce 值。
     extension_params: Box::new(PumpFunParams::from_trade(&trade_info, None)),
     lookup_table_key: None,
     wait_transaction_confirmed: true,