The modulo operator was incorrectly assigned PREC_TERM precedence, making it
evaluate at the same level as + and -. This caused expressions like "13 + 1 % 7"
to parse as "(13 + 1) % 7" instead of the correct "13 + (1 % 7)".
Changed the grammar rule for TOKEN_PERCENT to use PREC_FACTOR, matching the
precedence of * and / operators. Added a precedence test case in mod.wren to
verify the fix.