fix: use deterministic benchmark contribution data (JhaSourav07#1720)

## Summary

This PR makes the benchmark dataset deterministic by replacing random
contribution generation with a predictable calculation.

### Changes Made

* Added a deterministic contribution count generator
* Removed `Math.random()` from benchmark dataset creation
* Preserved variation in contribution values while ensuring
reproducibility

### Problem

The benchmark previously generated a different dataset on every
execution, making performance comparisons less reliable.

### Result

Benchmark runs now use a consistent dataset, improving reproducibility
and regression tracking.

Closes JhaSourav07#1678

Author: JhaSourav07

scripts/benchmark-svg.ts

@@ -18,11 +18,15 @@ const baseParams = {
   speed: sanitizeSpeed('8s'),
 };
 
+const deterministicContributionCount = (weekIndex: number, dayIndex: number): number => {
+  return ((weekIndex * 7 + dayIndex) * 13) % 20;
+};
+
 const calendar = {
   totalContributions: 1240,
   weeks: Array.from({ length: 14 }, (_, weekIndex) => ({
     contributionDays: Array.from({ length: 7 }, (_, dayIndex) => ({
-      contributionCount: Math.floor(Math.random() * 20),
+      contributionCount: deterministicContributionCount(weekIndex, dayIndex),
       date: `2026-05-${String(weekIndex * 7 + dayIndex + 1).padStart(2, '0')}`,
     })),
   })),