feat(backup): wrapper de stockage S3 (boto3) + faux stockage de test (#89)

tests/backup/fakes.py

@@ -0,0 +1,15 @@
+class FakeStorage:
+    def __init__(self):
+        self.objects: dict[str, bytes] = {}
+
+    def upload_bytes(self, key, data):
+        self.objects[key] = data
+
+    def download_bytes(self, key):
+        return self.objects[key]
+
+    def list_keys(self, prefix):
+        return [k for k in self.objects if k.startswith(prefix)]
+
+    def delete(self, key):
+        self.objects.pop(key, None)