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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src/constants/swqos.rs

@@ -323,6 +323,19 @@ pub const SWQOS_ENDPOINTS_ASTRALANE_QUIC: [&str; 8] = [
     "lim.gateway.astralane.io:7000", // Default
 ];
 
+/// Astralane QUIC MEV-protected endpoints (port 9000). Same region order as SWQOS_ENDPOINTS_ASTRALANE_QUIC.
+/// Use these when mev_protection=true to route through Astralane's MEV-protected path.
+pub const SWQOS_ENDPOINTS_ASTRALANE_QUIC_MEV: [&str; 8] = [
+    "ny.gateway.astralane.io:9000",  // NewYork
+    "fr.gateway.astralane.io:9000",  // Frankfurt
+    "ams.gateway.astralane.io:9000", // Amsterdam
+    "lim.gateway.astralane.io:9000", // SLC (no slc, use lim)
+    "sg.gateway.astralane.io:9000",  // Tokyo (Asia)
+    "ams.gateway.astralane.io:9000", // London (Europe)
+    "la.gateway.astralane.io:9000",  // LosAngeles
+    "lim.gateway.astralane.io:9000", // Default
+];
+
 pub const SWQOS_ENDPOINTS_STELLIUM: [&str; 8] = [
     "http://ewr1.flashrpc.com",
     "http://fra1.flashrpc.com",