fix(sankey): declare loop counter locally; add draftlog

The inner loop reused the file-scope `i` before its var declaration
line, tripping biome's noInvalidUseBeforeDeclaration, and the PR was
missing its changelog draftlog entry.

Author: CAOShurong

draftlogs/7977_fix.md

@@ -0,0 +1 @@
+ - Fix `node.pad` reduction warning so it derives the effective (post-clamp) padding from the laid-out node geometry instead of reading `sankey.nodePadding()`, which since @plotly/d3-sankey 0.12.x returns the configured value and made the warning never fire [[#7977](https://github.com/plotly/plotly.js/pull/7977)]

src/traces/sankey/render.js

@@ -89,8 +89,8 @@ function sankeyModel(layout, d, traceIndex) {
     });
     for(var key in columns) {
         var column = columns[key].sort(function(a, b) { return a[0] - b[0]; });
-        for(i = 1; i < column.length; i++) {
-            var gap = column[i][0] - column[i - 1][1];
+        for(var n = 1; n < column.length; n++) {
+            var gap = column[n][0] - column[n - 1][1];
             if(gap < effectivePad) effectivePad = gap;
         }
     }