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

**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:
```python
dpg.set_plot_axes(series_tag, x_axis=dpg.mvXAxis2, y_axis=dpg.mvYAxis1)
```

Or as optional parameters on series add functions:
```python
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