[BUG]: Sankey warning breaks in @plotly/d3-sankey v0.12.3

Description

The upgrade to @plotly/d3-sankey v0.12.3 (in #7830) will break the warning here:

if (sankey.nodePadding() < nodePad) {
    Lib.warn('node.pad was reduced to ', sankey.nodePadding(), ' to fit within the figure.');
}

In @plotly/d3-sankey@0.7.x, calling sankey.nodePadding() after running the layout returned the effective (post-clamp) padding value. In 0.12.3 the getter returns the user-configured value instead, because upstream split the internal state into separate dy (configured) and py (effective) variables.

After the upgrade, sankey.nodePadding() always equals nodePad, so the comparison is never true and the warning never fires. The layout itself still clamps correctly - only the diagnostic is affected.

Notes

Options to address the issue:

• Remove the warning entirely
• Derive the effective padding from the laid-out node positions (e.g. measure the gap between consecutive nodes in the densest column)

从 src/traces/sankey/render.js 中第 76-78 行附近的警告开始，然后将升级后的 @plotly/d3-sankey v0.12.3 padding API 与已布局的节点位置进行比较。确定应如何检测有效 padding，或者是否应移除警告，并验证诊断行为是否与被限制的布局一致。