fix/remove-custom-progressbar

[wyzula-jan]

Description

Since this widget is present in MainWindow, it should be rock solid. ScanProgressbar refactored to not use its own custom paintEvent based progress bar but rather native QProgressBar.

To avoid merge conflict I would prefer to merge after #1175

[github-actions]

Benchmark comparison

Threshold: 20% (lower is better).
Result: 0 regression(s), 0 improvement(s) beyond threshold.

No benchmark regression exceeded the configured threshold.

No benchmark improvement exceeded the configured threshold.

All benchmark results

Benchmark	Baseline	Current	Change	Status
BEC IPython client with companion app	5.91908 s	5.95395 s	+0.59%	ok
BEC IPython client without companion app	2.21378 s	2.12282 s	-4.11%	ok
Import bec_widgets	0.0143291 s	0.0125641 s	-12.32%	ok
tests/unit_tests/benchmarks/test_dock_area_benchmark.py::test_add_waveform_to_dock_area	0.151597 s	0.15354 s	+1.28%	ok