[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)

Inizia in src/traces/sankey/render.js, in corrispondenza dell'avviso intorno alle righe 76-78, quindi confronta l'API di padding aggiornata di @plotly/d3-sankey v0.12.3 con le posizioni dei nodi disposti. Determina come debba essere rilevato il padding effettivo o se l'avviso debba essere rimosso, e verifica che il comportamento diagnostico corrisponda al layout limitato.