Exact user-facing posit formatting

Ordinary posits print as exact decimals, using a decimal exponent for fractional values. The unique exceptional word is printed as NaR, matching the Posit Standard terminology. Formatting does not require a shortest decimal expansion; it preserves the exact value at every width.

def FloatLib.Floats.Formats.Posit.Model.display {format : Format} (value : Model format) : String

Host-independent display string of one posit value.

Ordinary values print through the exact decimal formatter; the unique exceptional word prints as NaR. There is no radix-two fallback. Formatting.Proof proves that parse recovers every input word, including NaR.

@[instance_reducible]

instance FloatLib.Floats.Formats.Posit.Model.instToString {format : Format} : ToString (Model format)