feat: add groupEventsByDate helper for schedule date headers

composeApp/src/commonTest/kotlin/ch/parano/myicek/filter/EventFilterTest.kt

@@ -20,6 +20,7 @@ package ch.parano.myicek.filter
 import ch.parano.myicek.models.Event
 import kotlin.test.Test
 import kotlin.test.assertEquals
+import kotlin.test.assertTrue
 
 class EventFilterTest {
 
@@ -28,6 +29,7 @@ class EventFilterTest {
         agegroup: String = "U13 (Elite)",
         name: String = "U13 Elite - HC Ajoie",
         eventType: String = "Jeu",
+        start: String = "2024-11-10T14:00:00",
     ) = Event(
         idEvent = id,
         agegroup = agegroup,
@@ -35,7 +37,7 @@ class EventFilterTest {
         title = "Title",
         opponent = "Opp",
         place = "Place",
-        start = "2024-11-10T14:00:00",
+        start = start,
         end = "2024-11-10T16:15:00",
         color = "#e4222e",
         eventType = eventType,
@@ -171,4 +173,47 @@ class EventFilterTest {
         assertEquals("U13 Elite", result[0])
         assertEquals("U13 Top", result[1])
     }
+
+    @Test
+    fun testGroupEventsByDateSingleDay() {
+        val events = listOf(
+            event(id = "1", start = "2024-11-10T14:00:00"),
+            event(id = "2", start = "2024-11-10T16:00:00"),
+        )
+        val grouped = groupEventsByDate(events)
+        assertEquals(1, grouped.size)
+        assertEquals("2024-11-10", grouped[0].first)
+        assertEquals(2, grouped[0].second.size)
+    }
+
+    @Test
+    fun testGroupEventsByDateMultipleDays() {
+        val events = listOf(
+            event(id = "1", start = "2024-11-11T10:00:00"),
+            event(id = "2", start = "2024-11-10T14:00:00"),
+            event(id = "3", start = "2024-11-10T16:00:00"),
+        )
+        val grouped = groupEventsByDate(events)
+        assertEquals(2, grouped.size)
+        assertEquals("2024-11-10", grouped[0].first)
+        assertEquals(2, grouped[0].second.size)
+        assertEquals("2024-11-11", grouped[1].first)
+        assertEquals(1, grouped[1].second.size)
+    }
+
+    @Test
+    fun testGroupEventsByDateWithSpaceSeparator() {
+        val events = listOf(
+            event(id = "1", start = "2024-11-10 14:00:00"),
+        )
+        val grouped = groupEventsByDate(events)
+        assertEquals(1, grouped.size)
+        assertEquals("2024-11-10", grouped[0].first)
+    }
+
+    @Test
+    fun testGroupEventsByDateEmpty() {
+        val grouped = groupEventsByDate(emptyList())
+        assertTrue(grouped.isEmpty())
+    }
 }