Expose `ImPlot::SetAxes()` to allow explicit X/Y axis pairing for plot series

[foodfo]

Description

Currently in DearPyGui, series can be added as children of any of the following axes — mvXAxis, mvXAxis2, mvXAxis3, mvYAxis, mvYAxis2, mvYAxis3 — but there is no way to explicitly control the pairing between X and Y axes for a given series.

It is not entirely clear to how DPG assigns axis pairings when multiple axes exist - the behavior appears inconsistent depending on which order the axes were created using dpg.add_plot_axis(), and what the hide/show state is when assigning via dpg.add_line_series(), etc.

It appears that the ImPlot API has supported explicit axis pairing since v0.13 via ImPlot::SetAxes(ImAxis x_idx, ImAxis y_idx), called immediately before each plot call. This is not currently exposed in DPG.

Proposed API

Expose this as an additional DPG method while leaving current default rank-based behavior intact. Users who do not call it get existing behavior. Users who need explicit control can override it:

dpg.set_plot_axes(series_tag, x_axis=dpg.mvXAxis2, y_axis=dpg.mvYAxis1)

Or as optional parameters on series add functions:

dpg.add_line_series(..., x_axis=dpg.mvXAxis2, y_axis=dpg.mvYAxis1)

Use Case

I'm building a multi-axis time series viewer where users drag and drop data columns onto specific axes. With explicit axis pairing exposed, when a user drags a series onto a specific axis I can detect how many alternative axes are currently enabled/visible and prompt the user to select the destination pairing — for example, drag onto Y2 and get a popup asking whether to plot against X1, X2, or X3. This is currently impossible because the pairing is assigned automatically with no way to override it after the fact.

Workarounds
I have not found reliable workarounds for the default behavior