[tests] Now test experiments with various combination of input sources

...core/test/prefix/algorithms/user/sum_over_channels/1.json

beat/core/test/prefix/algorithms/user/sum_over_channels/1.py

...core/test/prefix/algorithms/user/sum_over_channels/2.json

beat/core/test/prefix/algorithms/user/sum_over_channels/2.py

...core/test/prefix/algorithms/user/sum_over_channels/3.json

beat/core/test/prefix/algorithms/user/sum_over_channels/3.py

.../test/prefix/experiments/user/user/inputs_mix/1/test.json

.../test/prefix/experiments/user/user/inputs_mix/2/test.json

.../test/prefix/experiments/user/user/inputs_mix/3/test.json

...test/prefix/experiments/user/user/inputs_mix/3/test2.json

.../test/prefix/experiments/user/user/inputs_mix/4/test.json

...test/prefix/experiments/user/user/inputs_mix/4/test2.json

beat/core/test/prefix/toolchains/user/inputs_mix/1.json

beat/core/test/prefix/toolchains/user/inputs_mix/2.json

beat/core/test/prefix/toolchains/user/inputs_mix/3.json

beat/core/test/prefix/toolchains/user/inputs_mix/4.json

beat/core/test/test_execution.py