RoundRNE is not rounding to even, both logic and value side

[desmonddak]

Describe the bug

While the FP components match our conversion from double with rounding, the rounding algorithm is not truly RNE. RNE needs to consider the mantissa width; it looks like it is working correctly for odd lengths but not even.

To Reproduce

The bug won't reproduce on 32-bit because the RoundRNE is correct for odd mantissa lengths. So it needs to be validated by inspection and modifying both the value side and the logic side together.

Expected behavior

No response

Actual behavior

No response

Additional: Dart SDK info

No response

Additional: pubspec.yaml

Additional: Context

No response