test: cover the frame codec and command names

Builds SomfyFrame.cpp in the native env, with a minimal String and
no-op ESP_LOGx in the stubs, and tests:

- a fixed 56-bit frame, byte for byte, so what goes on air is pinned
- encode/decode round trips for 56-bit, 80-bit (repeats, Favorite,
  Stop, steps, Toggle), RTW and RTV frames
- rejection of bad checksums, addresses, rolling codes, keys and
  80-bit parity
- repeat/synonym tracking in copy()
- parsing and naming of commands

The command-name round trip fails: names the firmware reports, such as
"Step Up" and "My+Up", parse back to the wrong command.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/stubs/Arduino.h

@@ -9,6 +9,10 @@
 #include <cstdlib>
 #include <cstring>
 #include <ctime>
+#include <string>
+#include <type_traits>
+
+typedef uint8_t byte;
 
 // Fixed so anything formatted from it is deterministic.
 inline unsigned long millis() { return 0; }
@@ -17,4 +21,27 @@ inline bool getLocalTime(struct tm *info, uint32_t ms = 5000) {
   time_t now = time(nullptr);
   return localtime_r(&now, info) != nullptr;
 }
+
+// The parts of Arduino's String the firmware code under test uses.
+class String {
+  std::string _s;
+  public:
+    String() {}
+    String(const char *s) : _s(s ? s : "") {}
+    String(const std::string &s) : _s(s) {}
+    // Arduino formats integers in decimal.
+    template<typename T, typename std::enable_if<std::is_integral<T>::value, int>::type = 0>
+    explicit String(T val) : _s(std::to_string(val)) {}
+    const char *c_str() const { return _s.c_str(); }
+    unsigned int length() const { return (unsigned int)_s.length(); }
+    bool equalsIgnoreCase(const String &other) const {
+      if(_s.length() != other._s.length()) return false;
+      for(size_t i = 0; i < _s.length(); i++)
+        if(tolower((unsigned char)_s[i]) != tolower((unsigned char)other._s[i])) return false;
+      return true;
+    }
+    bool startsWith(const String &prefix) const { return _s.compare(0, prefix._s.length(), prefix._s) == 0; }
+    friend String operator+(const String &a, const String &b) { return String(a._s + b._s); }
+    friend bool operator==(const String &a, const String &b) { return a._s == b._s; }
+};
 #endif

test/stubs/esp_log.h

@@ -0,0 +1,10 @@
+// Logging stand-in for the native test env.  The format arguments are never
+// evaluated so tests stay quiet and logging can't affect what they check.
+#ifndef esp_log_stub_h
+#define esp_log_stub_h
+#define ESP_LOGE(tag, ...) ((void)(tag))
+#define ESP_LOGW(tag, ...) ((void)(tag))
+#define ESP_LOGI(tag, ...) ((void)(tag))
+#define ESP_LOGD(tag, ...) ((void)(tag))
+#define ESP_LOGV(tag, ...) ((void)(tag))
+#endif