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>

platformio.ini

@@ -101,7 +101,7 @@ lib_deps =
 platform = native
 test_framework = unity
 test_build_src = yes
-build_src_filter = -<*> +<Utils.cpp>
+build_src_filter = -<*> +<Utils.cpp> +<SomfyFrame.cpp>
 build_flags =
 	-std=gnu++17
 	-Isrc