Fix adding & removing children & parents

src/lib/components/test_cases/TestCaseEdit.svelte

@@ -122,16 +122,13 @@
 
   async function addPerson(id: string, isChild: boolean): Promise<void> {
     const entity = entityByKey[personEntityKey]
-    const personById = {
-      ...situation[entity.key_plural],
-    }
+    const personById = situation[entity.key_plural]
     const person = (personById[id] = {} as PopulationWithoutId)
     if (isChild) {
       person.date_naissance = {
         [year]: new Date(year - 10, 6, 2).toISOString().split("T")[0],
       }
     }
-    situation = { ...situation, [entity.key_plural]: personById }
 
     for (const groupEntity of Object.values(entityByKey) as GroupEntity[]) {
       if (groupEntity.is_person) {
@@ -472,18 +469,12 @@
   let personById = $derived(
     Object.fromEntries(persons.map((person) => [person.id, person])),
   )
-  let adultsId
-  run(() => {
-    adultsId = [
+  let adultsId = $state([
     ...Object.keys(personById).filter((id) => id.startsWith("Adulte ")),
-    ]
-  })
-  let childrenId
-  run(() => {
-    childrenId = [
+  ])
+  let childrenId = $state([
     ...Object.keys(personById).filter((id) => id.startsWith("Enfant ")),
-    ]
-  })
+  ])
   let adultSituations = $derived(
     Object.entries(situation[personEntity.key_plural] ?? {})
       .filter(([id]) => id.startsWith("Adulte "))