Stabilize hidden-GUI equal-axis fitting on macOS

[Copilot]

Hidden GUI / macOS was failing in GuiLayoutEisTest/eis_file_button_loads_selected_dta because equal-axis fitting occasionally used invalid/unstable UI axes pixel bounds, producing non-equal X/Y data-unit scaling. This PR hardens equalization geometry resolution to remove that transient failure mode.

• Root cause

  • Equal-data-unit fitting depended on a single getpixelposition(ax, true) read after drawnow.
  • In hidden macOS GUI runs, that read can transiently return unusable bounds, so equalization math is skipped or computed from unstable dimensions.

• Change

  • Updated +labkit/+app/+plot/private/finitePlotLimits.m to resolve axes pixel bounds via a dedicated helper before equalization:
    • retry pixel-position lookup across a few UI flush cycles;
    • fall back to ax.Position when pixel bounds are not yet usable.
  • Equal-axis span normalization now consumes this resolved geometry path.

• Behavioral impact

  • Keeps existing equal-data-units algorithm and API contract unchanged.
  • Reduces hidden-GUI platform timing sensitivity (notably macOS) in the EqualDataUnits=true path.

function position = resolveAxesPixelPosition(ax)
    for attempt = 1:3
        drawnow
        position = getpixelposition(ax, true);
        if numel(position) == 4 && position(3) > 0 && position(4) > 0
            return;
        end
    end
    fallback = ax.Position;
    if numel(fallback) == 4 && fallback(3) > 0 && fallback(4) > 0
        position = double(fallback);
    end
end