udisksbasejob: change samples heap allocation to stack

[GermanAizek]

References:

• https://publicwork.wordpress.com/2019/06/27/stack-allocation-vs-heap-allocation-performance-benchmark/
• https://stackoverflow.com/a/56798629

[tbzatek]

Jenkins, ok to test.

[tbzatek]

Well, this may look as an obvious candidate for microoptimization at first, but looking at how often the samples array is used, you'll realize this is a waste of precious memory (as you said yourself, RAM is very expensive nowadays!) in majority of the cases.

The point is that struct _UDisksBaseJobPrivate.samples array is only used in on_notify_progress() which gets connected only when the object property auto-estimate is set to TRUE (default = FALSE). Only the format-erase job uses that, as far as I was able to find.

So I wonder what was your point behind this - do you have some real world profiling numbers in hand supporting your changes?