feat: centralize MTU constants and fragmentation logic

- Created lib-network/src/mtu.rs with centralized MTU constants for all protocols
  - BLE: 23/247/512, chunk=200
  - Bluetooth Classic: 1000
  - LoRaWAN: 242
  - WiFi Direct: 1400
  - UDP: 1400, QUIC: 1200, Mesh: 65536
  - Added Protocol enum with mtu(), chunk_size(), negotiated_mtu() methods

- Created lib-network/src/fragmentation.rs with unified fragmentation logic
  - fragment_message() for splitting payloads
  - reassemble_message() for combining fragments
  - FragmentReassembler for stateful streaming reassembly
  - Handles out-of-order fragments, duplicates, concurrent messages

- Updated 10 files to use centralized constants:
  - lib-network: blockchain_sync, bluetooth (gatt/mod/classic), lorawan, lorawan_hardware, discovery
  - lib-storage: dht/transport
  - zhtp: bluetooth_le, web4_stub

- Removed all hardcoded MTU values (247, 242, 1400, 1000, 512, 23)
- Added backward-compatible deprecated aliases in blockchain_sync
- All 16 tests passing, code compiles successfully

Author: PeterGRutherford

lib-network/src/blockchain_sync/mod.rs

@@ -46,13 +46,20 @@ use anyhow::Result;
 use lib_crypto::PublicKey;
 use crate::types::mesh_message::ZhtpMeshMessage;
 use crate::protocols::NetworkProtocol;
+use crate::mtu::{
+    BLE_CHUNK_SIZE, BLUETOOTH_CLASSIC_CHUNK_SIZE, WIFI_DIRECT_CHUNK_SIZE, DEFAULT_CHUNK_SIZE,
+};
 use std::time::Duration;
 
-/// Chunk sizes based on protocol capabilities
-pub const BLE_CHUNK_SIZE: usize = 200;       // Conservative for BLE GATT (247-byte MTU)
-pub const CLASSIC_CHUNK_SIZE: usize = 1000;  // Bluetooth Classic RFCOMM (larger MTU)
-pub const WIFI_CHUNK_SIZE: usize = 1400;     // WiFi Direct (can handle more)
-pub const DEFAULT_CHUNK_SIZE: usize = 200;   // Safe fallback
+/// Re-export chunk sizes for backward compatibility
+#[deprecated(since = "0.1.0", note = "Use crate::mtu::BLE_CHUNK_SIZE instead")]
+pub const BLE_CHUNK_SIZE_COMPAT: usize = BLE_CHUNK_SIZE;
+
+#[deprecated(since = "0.1.0", note = "Use crate::mtu::BLUETOOTH_CLASSIC_CHUNK_SIZE instead")]
+pub const CLASSIC_CHUNK_SIZE: usize = BLUETOOTH_CLASSIC_CHUNK_SIZE;
+
+#[deprecated(since = "0.1.0", note = "Use crate::mtu::WIFI_DIRECT_CHUNK_SIZE instead")]
+pub const WIFI_CHUNK_SIZE: usize = WIFI_DIRECT_CHUNK_SIZE;
 
 /// Security constraints - Original limits
 pub const MAX_CHUNK_BUFFER_SIZE: usize = 10_000_000;  // 10MB max buffer per request
@@ -82,11 +89,13 @@ pub const MAX_REQUESTS_PER_PEER: usize = 10;
 
 /// Get optimal chunk size for protocol
 pub fn get_chunk_size_for_protocol(protocol: &NetworkProtocol) -> usize {
+    use crate::mtu::Protocol;
+    
     match protocol {
-        NetworkProtocol::BluetoothLE => BLE_CHUNK_SIZE,
-        NetworkProtocol::BluetoothClassic => CLASSIC_CHUNK_SIZE,
-        NetworkProtocol::WiFiDirect => WIFI_CHUNK_SIZE,
-        NetworkProtocol::TCP | NetworkProtocol::UDP => WIFI_CHUNK_SIZE,
+        NetworkProtocol::BluetoothLE => Protocol::BluetoothLE.chunk_size(),
+        NetworkProtocol::BluetoothClassic => Protocol::BluetoothClassic.chunk_size(),
+        NetworkProtocol::WiFiDirect => Protocol::WiFiDirect.chunk_size(),
+        NetworkProtocol::TCP | NetworkProtocol::UDP => Protocol::Udp.chunk_size(),
         _ => DEFAULT_CHUNK_SIZE,
     }
 }

lib-network/src/discovery/lorawan_hardware.rs

@@ -346,7 +346,7 @@ async fn test_serial_lorawan_module(port: &str, chip_type: &str) -> Result<LoRaW
                             class_a: true,
                             otaa_support: true,
                             abp_support: true,
-                            max_payload_size: 242,
+                            max_payload_size: crate::mtu::LORAWAN_MAX_PAYLOAD,
                             spreading_factors: vec![7, 8, 9, 10, 11, 12],
                             ..Default::default()
                         },
@@ -376,7 +376,7 @@ async fn detect_i2c_lorawan(address: &str) -> Result<LoRaWANHardware> {
                 class_a: true,
                 otaa_support: true,
                 abp_support: true,
-                max_payload_size: 242,
+                max_payload_size: crate::mtu::LORAWAN_MAX_PAYLOAD,
                 spreading_factors: vec![7, 8, 9, 10, 11, 12],
                 ..Default::default()
             },
@@ -414,7 +414,7 @@ async fn detect_raspberry_pi_lorawan_hat() -> Result<LoRaWANHardware> {
                                 class_c: true,
                                 otaa_support: true,
                                 abp_support: true,
-                                max_payload_size: 242,
+                                max_payload_size: crate::mtu::LORAWAN_MAX_PAYLOAD,
                                 spreading_factors: vec![7, 8, 9, 10, 11, 12],
                                 ..Default::default()
                             },
@@ -445,7 +445,7 @@ fn create_sx127x_hardware(chip_name: &str, spi_path: &str) -> LoRaWANHardware {
             class_c: true,
             otaa_support: true,
             abp_support: true,
-            max_payload_size: 242,
+            max_payload_size: crate::mtu::LORAWAN_MAX_PAYLOAD,
             spreading_factors: vec![6, 7, 8, 9, 10, 11, 12],
             ..Default::default()
         },
@@ -466,7 +466,7 @@ fn create_sx130x_hardware(chip_name: &str, spi_path: &str) -> LoRaWANHardware {
             class_c: true,
             otaa_support: true,
             abp_support: true,
-            max_payload_size: 242,
+            max_payload_size: crate::mtu::LORAWAN_MAX_PAYLOAD,
             spreading_factors: vec![7, 8, 9, 10, 11, 12],
             ..Default::default()
         },
@@ -509,7 +509,7 @@ async fn detect_windows_lorawan() -> Result<LoRaWANHardware> {
                     class_a: true,
                     otaa_support: true,
                     abp_support: true,
-                    max_payload_size: 242,
+                    max_payload_size: crate::mtu::LORAWAN_MAX_PAYLOAD,
                     spreading_factors: vec![7, 8, 9, 10],
                     ..Default::default()
                 },
@@ -559,7 +559,7 @@ async fn test_windows_com_lorawan(port_name: &str) -> Result<LoRaWANHardware> {
                             class_a: true,
                             otaa_support: true,
                             abp_support: true,
-                            max_payload_size: 242,
+                            max_payload_size: crate::mtu::LORAWAN_MAX_PAYLOAD,
                             spreading_factors: vec![7, 8, 9, 10],
                             ..Default::default()
                         },
@@ -632,7 +632,7 @@ async fn test_macos_usb_lorawan(device_path: &str) -> Result<LoRaWANHardware> {
                             class_a: true,
                             otaa_support: true,
                             abp_support: true,
-                            max_payload_size: 242,
+                            max_payload_size: crate::mtu::LORAWAN_MAX_PAYLOAD,
                             spreading_factors: vec![7, 8, 9, 10, 11, 12],
                             ..Default::default()
                         },