feat(companion_radio): add external FEM gain preferences for RX and TX for companions

Introduced consistent preferences for external LoRa FEM RX and TX gain settings in NodePrefs. Updated companion MyMesh to apply these settings during initialization and transmission. Added unit tests to verify the round-trip serialization of these new preferences.

test/test_config_serializer/test_config_serializer.cpp

@@ -1,6 +1,14 @@
 #include <gtest/gtest.h>
 #include "helpers/ConfigSerializer.h"
 
+class NativeFileSystem {
+public:
+    void mkdir(const char*) { }
+};
+#define FILESYSTEM NativeFileSystem
+#include "helpers/CommonCLI.h"
+#undef FILESYSTEM
+
 #define TEST_INT_S  "56"
 #define TEST_INT     56
 #define TEST_FLOAT_S  "-6.123"
@@ -21,6 +29,19 @@ public:
 class MockPrintStream : public Stream {
     int len = 0;
     uint8_t _buf[1024];
+
+    size_t printSigned(long long value) {
+        char text[24];
+        snprintf(text, sizeof(text), "%lld", value);
+        return Print::print(text);
+    }
+
+    size_t printUnsigned(unsigned long long value) {
+        char text[24];
+        snprintf(text, sizeof(text), "%llu", value);
+        return Print::print(text);
+    }
+
 public:
     size_t write(uint8_t b) override {
         if (len < sizeof(_buf)) {
@@ -30,17 +51,17 @@ public:
         return 0;
     }
 
-    size_t print(unsigned char b, int r) override { if (b == TEST_INT) return Print::print(TEST_INT_S); return 0; }
-    size_t print(int v, int r) override { if (v == TEST_INT) return Print::print(TEST_INT_S); return 0; }
-    size_t print(unsigned int v, int r) override { if (v == TEST_INT) return Print::print(TEST_INT_S); return 0; }
-    size_t print(long v, int r) override { if (v == TEST_INT) return Print::print(TEST_INT_S); return 0; }
-    size_t print(unsigned long v, int r) override { if (v == TEST_INT) return Print::print(TEST_INT_S); return 0; }
-    size_t print(long long v, int r) override { if (v == TEST_INT) return Print::print(TEST_INT_S); return 0; }
-    size_t print(unsigned long long v, int r) override { if (v == TEST_INT) return Print::print(TEST_INT_S); return 0; }
-    size_t print(double v, int p = 2) override { 
-        if (p == 6) return Print::print(TEST_DOUBLE_S);
-        if (p == 4) return Print::print(TEST_FLOAT_S);
-        return 0;
+    size_t print(unsigned char v, int r) override { return printUnsigned(v); }
+    size_t print(int v, int r) override { return printSigned(v); }
+    size_t print(unsigned int v, int r) override { return printUnsigned(v); }
+    size_t print(long v, int r) override { return printSigned(v); }
+    size_t print(unsigned long v, int r) override { return printUnsigned(v); }
+    size_t print(long long v, int r) override { return printSigned(v); }
+    size_t print(unsigned long long v, int r) override { return printUnsigned(v); }
+    size_t print(double v, int p = 2) override {
+        char text[32];
+        snprintf(text, sizeof(text), "%.*f", p, v);
+        return Print::print(text);
     }
 
     int getLength() const { return len; }
@@ -171,6 +192,28 @@ TEST(ConfigSerializer, LoadSerial_IgnoreUnknowns) {
     EXPECT_TRUE(match);
 }
 
+TEST(NodePrefs, FemGainSettingsRoundTrip) {
+    NodePrefs saved;
+    saved.radio_fem_rxgain = 0;
+    saved.radio_fem_txgain = 1;
+
+    MockPrintStream output;
+    ASSERT_TRUE(saved.saveSerial(output));
+
+    std::string serialised(reinterpret_cast<const char*>(output.getBytes()), output.getLength());
+    EXPECT_NE(std::string::npos, serialised.find("fem_rxgain:0"));
+    EXPECT_NE(std::string::npos, serialised.find("fem_txgain:1"));
+
+    MockInputStream input(serialised.c_str());
+    NodePrefs loaded;
+    loaded.radio_fem_rxgain = 1;
+    loaded.radio_fem_txgain = 0;
+
+    ASSERT_TRUE(loaded.loadSerial(input));
+    EXPECT_EQ(0, loaded.radio_fem_rxgain);
+    EXPECT_EQ(1, loaded.radio_fem_txgain);
+}
+
 
 // ── main ───────────────────────────────────────────────────────