Dispatch instance for exact logarithmic multiplication

The ordinary ExecFloat multiplication interface selects the certified direct logarithmic kernel.

@[instance_reducible, always_inline]

instance FloatLib.Floats.ExecFloat.Logarithmic.instMulFamily {radix : Numerics.Radix} [planning : Backend.PolicyFor (Family radix)] : Mul (Family radix)

Exact logarithmic multiplication participates in ordinary ExecFloat dispatch.