Function test_pow_exactly_one_impl

tests/fl/math/fixed_point.cpp:5146–5154

// thanks to the `base == one` short-circuit, but lock it in.
template <typename FP>
static void test_pow_exactly_one_impl() {
    const FP one(1.0f);
    const FP two(2.0f);
    const FP gamma_2_8(2.8f);
    const FP gamma_3_2(3.2f);
    FL_CHECK_EQ(FP::pow(one, two).raw(), one.raw());
    FL_CHECK_EQ(FP::pow(one, gamma_2_8).raw(), one.raw());
    FL_CHECK_EQ(FP::pow(one, gamma_3_2).raw(), one.raw());
}

// pow(base, exp) where base.raw() == SCALE - 1 (one ULP below 1.0). Without
// the snap, the polynomial gives a value ~50-100 LSB below expected. With