Refactor to consolidate APIs into contract package and introduce NFT interface for better modularity and maintainability.

contract/command.go

@@ -0,0 +1,12 @@
+package contract
+
+// Run is a function that executes nft command.
+type Run func(arg ...string) error
+
+type Command interface {
+	// Run nft command.
+	Run(arg ...string) error
+
+	// RunWithOutput Run nft command with output.
+	RunWithOutput(arg ...string) (string, error)
+}