Fix data_consumer generator exhaustion when decorators are stacked

[paveldedik]

A generator expression passed to @data_consumer is a one-shot iterator. When stacked decorators create an outer loop, the inner generator was fully consumed on the first pass and silently yielded nothing on subsequent passes, dropping test combinations without any error.

Fix: materialize generator arguments into lists at decoration time so they can be re-iterated for each outer-loop pass.

[paveldedik]

Before the fix, this is how it behaved:

@data_consumer([True, False], _output_name='flag')
@data_consumer((x for x in [1, 2, 3]), _output_name='number')
def test_something(self, number, flag):
   print(number, flag)

It would print:

1 True
2 True
3 True

The workaround would be using a list comprehension instead of a generator:

@data_consumer([x for x in [1, 2, 3]], _output_name='number')

Anyway, after this fix, it works just fine:

1 True
2 True
3 True
1 False
2 False
3 False