New unity component can be used for testing other applications.
Upstream version of Unity is included as a submodule.
Utilities specific to ESP-IDF unit tests (partitions, leak checking
setup/teardown functions, etc) are kept only in unit-test-app.
Kconfig options are added to allow disabling certain Unity features.
current unit-test-app don't support test components need to communicate
with each other (like GPIO, SPI ...). Now we add multiple devices mode
to unit test app, support writing and running test with multiple DUTs.
please refer to `docs/api-guides/unit-tests.rst` for detail.