TTS-only presets cannot build with NEMO_SPEECH_BUILD_TESTS=ON

tests/cpp/CMakeLists.txt adds the tts subdirectory whenever NEMO_SPEECH_BUILD_TTS is on, but tests/cpp/tts/CMakeLists.txt adds test_magpietts_asr unconditionally and links nemo_speech_asr and tests_cpp_wer. Neither exists in a TTS-only build, so configuration succeeds and the build then fails.

Reproduced on main (69d7fd4), macOS 26.6.2:

scripts/configure.sh cpu-tts -DNEMO_SPEECH_BUILD_TESTS=ON
cmake --build build/cpu-tts

tests/cpp/tts/test_magpietts_asr.cpp:22:10: fatal error: 'recognizer.h' file not found
   22 | #include "recognizer.h"  // RecognizerConfig

Not platform-specific: cpu-tts and metal-tts both reproduce it. CI does not catch it because the macOS job builds metal-speech, which has ASR on.

The fix looks like guarding that target the way test_magpietts_cached_attention is guarded twelve lines above:

if(NEMO_SPEECH_BUILD_ASR)
    add_executable(test_magpietts_asr test_magpietts_asr.cpp)
    ...
endif()

I have checked that this builds cpu-tts with tests enabled, and that cpu-speech still produces test_magpietts_asr. PR to follow.

Start in tests/cpp/tts/CMakeLists.txt, comparing test_magpietts_asr with the guarded test_magpietts_cached_attention target. Configure and build the cpu-tts test setup, then verify that the TTS-only build succeeds while the cpu-speech build still produces test_magpietts_asr.