Fixing the convoluted `._set_yrange()` callbacks mess

[goodboy]

Qt has messy stuff like "signals and slots" which actually provide not much benefit when used from python (since calling python from C++ doesn't often 😂) which we originally used to fall in line with the default architecture of pyqtgraph's ViewBox.

Trying to understand how all these signals and slots fit together is a nightmare even for me who's hacked pretty hard on the core of it all and I still get confused every time i come back to the code responsible even with the recent major refactoring to our Flows abstraction layer..

This was overall a major annoyance and source of misunderstanding in recent work for solving y-range sorting performance enhancements in #342.

So what do we do to start addressing this?

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high level breakdown.. of the mess

to begin groking these are notable bits in the code base to know about:

• ChartView._set_yrange() is triggered by interactions with any view: basically Qt's graphics scene parlance for some multi-"canvas" window into a backing data set domain.
• multiple views can be overlayed on a PlotItem via our PlotItemOverlay and thus despite having a view "in focus" often we need to figure out the y-range of all overlayed (eg. in the case of FSPs with a common y-range domain) time series, what we call Flow's to ack the real-time bits, and thus we have to consider updating such overlays in our main interaction callback: .maybe_downsample_graphics()
• .set_yrange() in turn calls into ChartView._maxmin(), a custom callback which we by default make delegate to a similar method on the containing ChartPlotWidget.maxmin(), and
• this method in turn calls Flow.maxmin() for the named, contained target flow which in turn does all the hard work of computing and caching max/mins..

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How this works going forward: TODO: fill this out!

• slew of commits are here but i will ideally link to specific breakdown via commits msgs soon.
• we don't use Signal handlers to update every individual view box, instead we have a single handler which iterates all overlays and linked charts (with caveats)
• we are going to provide for an optional "incrementally updated by stream" style API so that the quote-stream driven display loop can avoid re-sorts of data that is being only updated with a single new datum.

[goodboy]

Soo turns out I already solved most of this without doing a writeup 😸

The slew of commits are here: https://github.com/pikers/piker/commits/534f96e8d7824d1e56c08705e713e136ed1ef69a/piker/ui/_interaction.py and more or less starting @ https://github.com/pikers/piker/commit/1782bb7d22fbbde548bb78822f7e78b47de14136.

Likely this change set will get factored into a more compact PR so i'll follow up if and when.

[goodboy]

Yeah, mostly resolved in the work from #453 and #455 🥳

[goodboy]

Pretty sure #455 fill finish off the rest of this since we will be entirely bypassing the whole Signal junk after that lands 🏄🏼