fix: use bracket notation for index signature properties (TS4111)

Fix TypeScript TS4111 errors in frame.ts, series.ts, and style.ts by
replacing dot notation with bracket notation for properties accessed
from index signatures.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

src/core/frame.ts

@@ -779,7 +779,7 @@ function isIndexLike(v: unknown): v is Index<Label> {
   }
   const rec = v as Record<string, unknown>;
   return (
-    typeof rec.size === "number" && typeof rec.at === "function" && typeof rec.getLoc === "function"
+    typeof rec["size"] === "number" && typeof rec["at"] === "function" && typeof rec["getLoc"] === "function"
   );
 }
 

src/core/series.ts

@@ -1036,6 +1036,6 @@ function isIndexLike(v: unknown): v is Index<Label> {
   }
   const rec = v as Record<string, unknown>;
   return (
-    typeof rec.size === "number" && typeof rec.at === "function" && typeof rec.getLoc === "function"
+    typeof rec["size"] === "number" && typeof rec["at"] === "function" && typeof rec["getLoc"] === "function"
   );
 }

src/stats/style.ts

@@ -257,7 +257,7 @@ function colormapColor(t: number, cmap: string): string {
     const parts = cmap.split(":");
     return lerpColor(parts[0] ?? "#ffffff", parts[1] ?? "#000000", t);
   }
-  const stops = COLORMAPS[cmap] ?? COLORMAPS.Blues!;
+  const stops = COLORMAPS[cmap] ?? COLORMAPS["Blues"]!;
   // Find surrounding stops
   for (let i = 0; i < stops.length - 1; i++) {
     const [p0, c0] = stops[i]!;