refactor: split MeshTables::hasSeen into pure query + markSeen

hasSeen() was simultaneously a predicate and a mutator — it inserted the
packet hash on every miss, making five call sites that only wanted to mark
a packet as sent call it with the return value discarded.

Split into:
- wasSeen()   — pure predicate, no side effects
- markSeen()  — explicit insert

All query sites now call markSeen() immediately after wasSeen() returns
false, preserving identical runtime behaviour. The five mark-only send
sites (sendFlood, sendDirect, sendZeroHop x2) now call markSeen directly.

Also fixes three bridge sites (BridgeBase, ESPNowBridge, RS232Bridge)
that had the same query+implicit-insert pattern.

Tests: add test/test_mesh_tables/ covering wasSeen purity, markSeen,
dup stats, and clear. Update SHA256 mock to produce deterministic output
(previously finalize() was a no-op). Add Packet.cpp to native build filter.

src/helpers/SimpleMeshTables.h

@@ -31,27 +31,31 @@ public:
   }
 #endif
 
-  bool hasSeen(const mesh::Packet* packet) override {
+  bool wasSeen(const mesh::Packet* packet) override {
     uint8_t hash[MAX_HASH_SIZE];
     packet->calculatePacketHash(hash);
 
     const uint8_t* sp = _hashes;
     for (int i = 0; i < MAX_PACKET_HASHES; i++, sp += MAX_HASH_SIZE) {
-      if (memcmp(hash, sp, MAX_HASH_SIZE) == 0) { 
+      if (memcmp(hash, sp, MAX_HASH_SIZE) == 0) {
         if (packet->isRouteDirect()) {
-          _direct_dups++;   // keep some stats
+          _direct_dups++;
         } else {
           _flood_dups++;
         }
         return true;
       }
     }
-
-    memcpy(&_hashes[_next_idx*MAX_HASH_SIZE], hash, MAX_HASH_SIZE);
-    _next_idx = (_next_idx + 1) % MAX_PACKET_HASHES;  // cyclic table
     return false;
   }
 
+  void markSeen(const mesh::Packet* packet) override {
+    uint8_t hash[MAX_HASH_SIZE];
+    packet->calculatePacketHash(hash);
+    memcpy(&_hashes[_next_idx * MAX_HASH_SIZE], hash, MAX_HASH_SIZE);
+    _next_idx = (_next_idx + 1) % MAX_PACKET_HASHES;
+  }
+
   void clear(const mesh::Packet* packet) override {
     uint8_t hash[MAX_HASH_SIZE];
     packet->calculatePacketHash(hash);

src/helpers/bridges/BridgeBase.cpp

@@ -39,7 +39,8 @@ void BridgeBase::handleReceivedPacket(mesh::Packet *packet) {
     return;
   }
 
-  if (!_seen_packets.hasSeen(packet)) {
+  if (!_seen_packets.wasSeen(packet)) {
+    _seen_packets.markSeen(packet);
     // bridge_delay provides a buffer to prevent immediate processing conflicts in the mesh network.
     _mgr->queueInbound(packet, millis() + _prefs->bridge_delay);
   } else {

src/helpers/bridges/BridgeBase.h

@@ -110,7 +110,7 @@ protected:
    * @brief Common packet handling for received packets
    *
    * Implements the standard pattern used by all bridges:
-   * - Check if packet was seen before using _seen_packets.hasSeen()
+   * - Check if packet was seen before using _seen_packets.wasSeen()
    * - Queue packet for mesh processing if not seen before
    * - Free packet if already seen to prevent duplicates
    *

src/helpers/bridges/ESPNowBridge.cpp

@@ -167,7 +167,8 @@ void ESPNowBridge::sendPacket(mesh::Packet *packet) {
     return;
   }
 
-  if (!_seen_packets.hasSeen(packet)) {
+  if (!_seen_packets.wasSeen(packet)) {
+    _seen_packets.markSeen(packet);
     // Create a temporary buffer just for size calculation and reuse for actual writing
     uint8_t sizingBuffer[MAX_PAYLOAD_SIZE];
     uint16_t meshPacketLen = packet->writeTo(sizingBuffer);

src/helpers/bridges/RS232Bridge.cpp

@@ -115,7 +115,8 @@ void RS232Bridge::sendPacket(mesh::Packet *packet) {
     return;
   }
 
-  if (!_seen_packets.hasSeen(packet)) {
+  if (!_seen_packets.wasSeen(packet)) {
+    _seen_packets.markSeen(packet);
 
     uint8_t buffer[MAX_SERIAL_PACKET_SIZE];
     uint16_t len = packet->writeTo(buffer + 4);