rename json artifact to package + update resolver integrity checks

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

syft/source/all_layers_resolver.go

@@ -8,7 +8,7 @@ import (
 	"github.com/anchore/stereoscope/pkg/image"
 )
 
-var _ Resolver = &AllLayersResolver{}
+var _ Resolver = (*AllLayersResolver)(nil)
 
 // AllLayersResolver implements path and content access for the AllLayers source option for container image data sources.
 type AllLayersResolver struct {

syft/source/directory_resolver.go

@@ -11,7 +11,7 @@ import (
 	"github.com/bmatcuk/doublestar"
 )
 
-var _ Resolver = &DirectoryResolver{}
+var _ Resolver = (*DirectoryResolver)(nil)
 
 // DirectoryResolver implements path and content access for the directory data source.
 type DirectoryResolver struct {

syft/source/image_squash_resolver.go

@@ -7,7 +7,7 @@ import (
 	"github.com/anchore/stereoscope/pkg/image"
 )
 
-var _ Resolver = &ImageSquashResolver{}
+var _ Resolver = (*ImageSquashResolver)(nil)
 
 // ImageSquashResolver implements path and content access for the Squashed source option for container image data sources.
 type ImageSquashResolver struct {