Simplify date util function using date-fns and make simple tests

apps/app/src/server/util/contribution-graph-utils.ts

@@ -1,40 +0,0 @@
-/**
- * Gets current week's ISO week ID, e.g 2025-W32
- */
-export const getISOWeekId = (date: Date): string => {
-  const utcDate = new Date(Date.UTC(date.getFullYear(), date.getMonth(), date.getDate()));
-  const dayNum = utcDate.getUTCDay() || 7;
-  utcDate.setUTCDate(utcDate.getUTCDate() + 4 - dayNum);
-
-  const yearStart = new Date(Date.UTC(utcDate.getUTCFullYear(), 0, 1));
-  const diffInMs = utcDate.getTime() - yearStart.getTime();
-  const oneDayInMs = 86400000;
-  const weekNumber = Math.ceil(((diffInMs / oneDayInMs) + 1) / 7);
-  const weekString = String(weekNumber).padStart(2, '0');
-
-  const year = utcDate.getUTCFullYear();
-  const weekId = `${year}-W${weekString}`;
-
-  return weekId;
-};
-
-
-export const daysSinceLastUpdate = (
-    lastUpdateDate: Date,
-    currentDate: Date = new Date(),
-): number => {
-  const oneDayInMs = 86400000;
-  const diffInMs = currentDate.getTime() - lastUpdateDate.getTime();
-  const diffDays = Math.floor(diffInMs / oneDayInMs);
-
-  return Math.max(0, diffDays);
-};
-
-export const getCurrentWeekStart = (date: Date = new Date()): Date => {
-  const utcDate = new Date(Date.UTC(date.getFullYear(), date.getMonth(), date.getDate()));
-  const day = utcDate.getUTCDay();
-  const diff = (day === 0) ? 6 : day - 1;
-  utcDate.setUTCDate(utcDate.getUTCDate() - diff);
-
-  return utcDate;
-};