API: Automatically collect times and costs into single list

[carterbox]

The "cost" parameter has been renamed "costs" to be consistent with "times".

Previously the objective value at the end of each iteration was collected in a list then converted into a numpy array and appended. Now these lists (for iteration time and objective value) are assumed to be lists and directly appended each iteration.

Also fixed a bug where the cgrad method would sometimes return a cost that was not localized to host memory.

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