feat: Add RNTuple row extension and field addition via update mode

src/uproot/writing/_cascade.py

@@ -2145,7 +2145,7 @@ def deserialize(cls, raw_bytes, location):
         assert compression_code >= 0
         assert info_location >= 0
         assert info_num_bytes >= 0
-        assert uuid_version <= 8
+        assert 0 <= uuid_version <= 8
 
         out = FileHeader(
             end,

src/uproot/writing/_cascadentuple.py

@@ -242,21 +242,33 @@ def serialize(self):
 
 # https://github.com/root-project/root/blob/master/tree/ntuple/v7/doc/specifications.md#column-description
 class NTuple_Column_Description:
-    def __init__(self, type_num, bits_on_disk, field_id, flags, repr_index):
+    def __init__(
+        self, type_num, bits_on_disk, field_id, flags, repr_index, first_element_index=0
+    ):
         self.type_num = type_num
         self.bits_on_disk = bits_on_disk
         self.field_id = field_id
         self.flags = flags
         self.repr_index = repr_index
+        self.first_element_index = first_element_index
 
     def serialize(self):
+        import uproot.const
+
+        flags = self.flags
+        if self.first_element_index > 0:
+            flags = flags | uproot.const.RNTupleColumnFlags.DEFERRED
         header_bytes = _rntuple_column_record_format.pack(
             self.type_num,
             self.bits_on_disk,
             self.field_id,
-            self.flags,
+            int(flags),
             self.repr_index,
         )
+        if self.first_element_index > 0:
+            import struct
+
+            header_bytes += struct.pack("<Q", int(self.first_element_index))
         return header_bytes