P3109 conversion capabilities

The destination quantizer uses the exact rational scalar domain and the existing ProjectionPolicy context. Context-free conversion selects FloatLib's nearest-even, no-saturation policy explicitly.

@[instance_reducible]

instance FloatLib.Floats.ExecFloat.P3109.Conversion.quantizer {format : Formats.P3109.Format} : Quantizer (P3109 format) ℚ

Every valid P3109 descriptor supports policy-aware exact-rational quantization.

@[instance_reducible]

instance FloatLib.Floats.ExecFloat.P3109.Conversion.defaultQuantizer {format : Formats.P3109.Format} : DefaultQuantizer (P3109 format) ℚ

Context-free P3109 conversion uses nearest-even rounding and no saturation request.