Implement blueprint update-append:
allow to push and pop fields at the end of the tuple,
without knowing the tuple size.

Use rope index to dynamically cut and paste fields
in a tuple.

Designate UINT32_MAX as a filed number for
tuple end. It's possible to SET or INSERT
fields at the end of the tuple, by specifying
field_no == UINT32_MAX. Delete
with field_no == UINT32_MAX deletes the last
field.

Add a test.