The function Fq2::mul_constant_by_fq_montgomery expects its constant argument to be in
standard form and converts it to Montgomery form internally within the function. This differs from
other field-operation functions involving constants, which expect their constant arguments to
already be in Montgomery form. This inconsistency is not properly documented.

We verified the current usage in src/gadgets/bn254/pairing.rs and confirmed the implementation
is correct; the arkworks coefficients passed as constants are in standard form, matching the function's expectation.