internal/pkg: pass context to file cure

This removes the left over embedded contexts.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/file.go

@@ -1,6 +1,7 @@
 package pkg
 
 import (
+	"context"
 	"crypto/sha512"
 )
 
@@ -31,4 +32,4 @@ func (a fileArtifact) Checksum() Checksum {
 }
 
 // Cure returns the caller-supplied data.
-func (a fileArtifact) Cure() ([]byte, error) { return a, nil }
+func (a fileArtifact) Cure(context.Context) ([]byte, error) { return a, nil }