feat(goctl/rpc): support external proto imports with cross-package ty… (#5472)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tools/goctl/rpc/parser/proto.go

@@ -2,12 +2,15 @@ package parser
 
 // Proto describes a proto file,
 type Proto struct {
-	Src       string
-	Name      string
-	Package   Package
-	PbPackage string
-	GoPackage string
-	Import    []Import
-	Message   []Message
-	Service   Services
+	Src           string
+	Name          string
+	Package       Package
+	PbPackage     string
+	GoPackage     string
+	Import        []Import
+	Message       []Message
+	Service       Services
+	// ImportedProtos holds the metadata for all transitively imported proto files.
+	// Populated by the generator before code generation.
+	ImportedProtos []ImportedProto
 }