Fix filled log plot auto-connect

[cookesan]

Summary

• keep filled PlotDataItem curves continuous when connect="auto" and log mode creates non-finite points
• add a seeded histogram regression for filled center-step plots in log Y mode

Fixes #2312.

Tests

• QT_QPA_PLATFORM=minimal .venv/bin/pytest tests/graphicsItems/test_PlotDataItem.py::test_filled_log_plot_auto_connects_across_nonfinite_values -q
• QT_QPA_PLATFORM=minimal .venv/bin/pytest tests/graphicsItems/test_PlotDataItem.py -q
• QT_QPA_PLATFORM=minimal .venv/bin/pytest tests/graphicsItems/test_PlotCurveItem.py -q
• QT_QPA_PLATFORM=minimal .venv/bin/pytest tests/graphicsItems -q
• .venv/bin/python -m compileall pyqtgraph/graphicsItems/PlotDataItem.py tests/graphicsItems/test_PlotDataItem.py
• git diff --check

[pijyoi]

#3071 implements filling under the curve when connect="finite". You can see how it works in the MouseSelection example.

It seems to me that in this PR, this drawing mode would be bypassed for all plots, Log mode or not?

[pijyoi]

Disregard the above comment. The logic in this PR only applies if connect="auto"

So the below snippet will work properly. i.e. break the curve into continuous segments and fill them.

import numpy as np

import pyqtgraph as pg

pg.mkQApp()
plt = pg.PlotWidget()

x = np.arange(0, 1000, dtype=float)
x[(250, 500, 750),] = np.nan
y=np.sin(np.linspace(1, 21, 1000))
plt.plot(x=x, y=y, pen='g', connect="finite", fillLevel=0, brush=(50,50,200,100))

plt.show()
pg.exec()