Store unit map attributes as vmvar_t and derive VR/VW transfer sizes
from their element type. This prevents buffer overruns after vmvar_t
became uint16_t and fixes upward movement in Rance IV.
Add scenario coverage for both transfer directions and verify that
adjacent variables remain intact.
Cover variable page allocation, array reference handling, and Shift-JIS
conversion in src_tests.
Extend the scenario suite with 16-bit boundary behavior for assignments,
loops, module results, and save/load round trips.
kichikuou