#1388 pgtype.Range json marshal and unmarshal

[acim]

No description provided.

[jackc]

Is it possible to reuse some more of the existing text encoding and parsing code? I haven't looked at it in detail, but naively I would have assumed that MarshalJSON would basically delegate to the existing text format encoding code and UnmarshalJSON would basically delegate to the existing text format parsing code.

[acim]

I could reuse parseUntypedTextRange in UnmarshalJSON, but reusing Encode method of encodePlanRangeCodecRangeValuerToText struct looks not an easy thing to do because it's using type OID's for which I don't see the way to get in func (src Range[T]) MarshalJSON() ([]byte, error) since T in Range is of type any. There are no further bounds, so getting an OID seems impossible.

		lowerPlan := plan.m.PlanEncode(plan.rc.ElementType.OID, TextFormatCode, lower)
		if lowerPlan == nil {
			return nil, fmt.Errorf("cannot encode %v as element of range", lower)
		}

		buf, err = lowerPlan.Encode(lower, buf)
		if err != nil {
			return nil, fmt.Errorf("failed to encode %v as element of range: %v", lower, err)
		}
		if buf == nil {
			return nil, fmt.Errorf("Lower cannot be NULL unless LowerType is Unbounded")
		}

and the similar piece of code for upper bound in case of json could be simple replaced by marshal. So the only useful code from there would be before and after these mentioned.

[acim]

Actually, I found a way to reuse the encodePlanRangeCodecRangeValuerToText.Encode but I had to modify it to:

type encodePlanRangeCodecRangeValuerToText struct {
	rc Codec
	m  interface {
		PlanEncode(oid uint32, format int16, value any) EncodePlan
	}
}

I implemented tests for Range[Date] and Range[Numeric] and then found out that Numeric didn't have json.Unmarshaler implementation so I did that also. I couldn't run all tests because lot of them require database connection. @jackc, could you please allow CI to run for this PR?