feat: add global MEV protection and refactor TradeConfig to builder pattern

- Add `mev_protection: bool` to `TradeConfig` and `InfrastructureConfig` (default: false)
  - Astralane QUIC: switches to port 9000 (MEV-protected endpoint) when enabled
  - BlockRazor HTTP: uses `mode=sandwichMitigation` query param when enabled
  - BlockRazor gRPC: uses `mode=sandwichMitigation` when enabled
- Add `SWQOS_ENDPOINTS_ASTRALANE_QUIC_MEV` constants (port 9000) to `constants/swqos.rs`
- Fix `astralane_quic.rs` IP candidates to use the actual port from the address (supports both 7000 and 9000)
- Refactor `TradeConfig` to builder pattern via `TradeConfig::builder()`
  - Introduce `TradeConfigBuilder` with all optional fields and clear defaults
  - `TradeConfig::new()` kept as a shortcut (calls `builder().build()`) for backward compatibility
  - Remove old `with_wsol_ata_config` / `with_check_min_tip` / `with_swqos_cores_from_end` / `with_mev_protection` chain methods
- Update all 16 examples to use `TradeConfig::builder()` with commented-out options so users can discover all available settings at a glance
- Update README.md and README_CN.md code snippets to use builder pattern

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examples/nonce_cache/src/main.rs

@@ -108,7 +108,14 @@ async fn create_solana_trade_client() -> AnyResult<SolanaTrade> {
     let rpc_url = "https://api.mainnet-beta.solana.com".to_string();
     let commitment = CommitmentConfig::confirmed();
     let swqos_configs: Vec<SwqosConfig> = vec![SwqosConfig::Default(rpc_url.clone())];
-    let trade_config = TradeConfig::new(rpc_url, swqos_configs, commitment);
+    let trade_config = TradeConfig::builder(rpc_url, swqos_configs, commitment)
+        // .create_wsol_ata_on_startup(true)  // default: true
+        // .use_seed_optimize(true)            // default: true
+        // .log_enabled(true)                  // default: true
+        // .check_min_tip(false)               // default: false
+        // .swqos_cores_from_end(false)        // default: false
+        // .mev_protection(false)              // default: false
+        .build();
     let solana_trade = SolanaTrade::new(Arc::new(payer), trade_config).await;
     println!("✅ SolanaTrade client initialized successfully!");
     Ok(solana_trade)