Better handling of metadata

[solvicode]

The metadata handling in the Go SDK is not great:

func deviationDetector(params *orca.ExecutionParams) (orca.Result, error) {
	var p_h float64 = Config.PriorOnReset
	var p_h_e float64 = Config.PriorOnReset

	var currentWindow = params.Window
	var metadata = make(map[string]any, len(NewDatapoint.MetadataFields))
	for _, field := range NewDatapoint.MetadataFields {
		val, ok := currentWindow.Metadata[field.Name]
		if !ok {
			return nil, fmt.Errorf("expected field %v", field.Name)
		}
		metadata[field.Name] = val
	}
	currentVector, ok := metadata[VECTOR_FIELD_NAME]
	if !ok {
		return nil, fmt.Errorf("could not retreived the current vector. looking for %v", VECTOR_FIELD_NAME)
	}

	vLowPrec, ok := currentVector.(structpb.ListValue)
...

I don't want to have to manually parse out the struct PB values. I should expect the fields to be there... Perhaps we can do this validation behind the scenes in the SDK?

[solvicode]

This is the function that needs changing:

func NewExecutionParams(window *contract.Window, deps *Dependencies, selfResults []*DependencyResultRow) *ExecutionParams {
	metadata := make(map[string]any)
	if window.Metadata != nil {
		metadata = window.Metadata.AsMap()
	}

	return &ExecutionParams{
		Window: Window{
			TimeFrom: window.TimeFrom.AsTime(),
			TimeTo:   window.TimeTo.AsTime(),
			Name:     window.WindowTypeName,
			Version:  window.WindowTypeVersion,
			Origin:   window.Origin,
			Metadata: metadata,
		},
		Dependencies: deps,
		SelfResults:  selfResults,
	}
}

[solvicode]

And generics will also be required on the MetadataField struct.

[solvicode]

This way, when defining it we can capture the type. But this will need to be parsed into the protobuf struct also - requiring a update to the contract repo.