Fixes #7832.

Problem

The warning in src/traces/sankey/render.js compared sankey.nodePadding() against the configured node.pad. Since the upgrade to @plotly/d3-sankey@0.12.3 (#7830), that getter returns the configured value — the post-clamp padding is kept in an internal variable (py, computed in computeNodeBreadths) and never exposed:

if(sankey.nodePadding() < nodePad) {   // always false since v0.12
    Lib.warn('node.pad was reduced to ', sankey.nodePadding(), ' ...');
}

So after #7830 users are no longer warned when their node.pad is clamped to fit the figure. The layout itself still clamps correctly; only the diagnostic broke.

Fix

Measure the effective padding from the laid-out node positions instead of asking the generator: group nodes by column (x0 when horizontal, else y0), sort each column along its position axis, and take the smallest gap between consecutive nodes. This reflects the post-clamp padding and works identically for both @plotly/d3-sankey and @plotly/d3-sankey-circular (whose getter has the same configured-value behavior). The warning now reports the effective value rounded to 2 decimals.

Verification

• Reproduced the getter semantics change directly against installed @plotly/d3-sankey@0.12.3: a graph needing a clamp reports nodePadding() === 50 (the configured value) while laid-out gaps are far smaller — same for @plotly/d3-sankey-circular@0.33.1.
• New jasmine tests in test/jasmine/tests/sankey_test.js (node.pad clamp warning (issue 7832)):
  • a cramped layout fires exactly one node.pad was reduced warning — PASS
  • a roomy layout stays silent — PASS
• The pre-existing sankey drag/hover interaction specs fail on this branch and on clean upstream/master alike (mouse-event timeouts in this environment); all non-interaction specs including the two new ones pass.