add kmeans, moving-average, temporal functions, retail functions

add 
1. "ml/kmeans" (kmeans.ts) 
2. "series/moving-average" (time-helper.ts)
3. "time/week-number", "time/same-day-last-year" (time-helper.ts)
4. 購買率"retail/purchase-rate", リフト値"retail/lift-value", 原価率"retail/cost-ratio" 値入り率"retail/gross-margin" (server.ts)

time-helper.ts

@@ -0,0 +1,24 @@
+// time-helpers.ts - Date and time utility functions
+
+import { getISOWeek, getISODay, subYears, setISOWeek, setISODay, isValid } from 'date-fns';
+
+export const getWeekNumber = (dateString: string): number => {
+  const date = new Date(dateString);
+  if (!isValid(date)) {
+    throw new Error('Invalid date string provided.');
+  }
+  return getISOWeek(date);
+};
+
+export const getSameWeekDayLastYear = (dateString: string): string => {
+  const baseDate = new Date(dateString);
+  if (!isValid(baseDate)) {
+      throw new Error('Invalid date string provided.');
+  }
+  const originalWeek = getISOWeek(baseDate);
+  const originalDayOfWeek = getISODay(baseDate);
+  const lastYearDate = subYears(baseDate, 1);
+  const dateWithWeekSet = setISOWeek(lastYearDate, originalWeek);
+  const finalDate = setISODay(dateWithWeekSet, originalDayOfWeek);
+  return finalDate.toISOString().split('T')[0]; // Return as YYYY-MM-DD
+};