feat(plugins): add SubsonicAPI CallRaw, with support for raw=true binary response for host functions (#4982)

* feat: implement raw binary framing for host function responses

Signed-off-by: Deluan <deluan@navidrome.org>

* feat: add CallRaw method for Subsonic API to handle binary responses

Signed-off-by: Deluan <deluan@navidrome.org>

* test: add tests for raw=true methods and binary framing generation

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: improve error message for malformed raw responses to indicate incomplete header

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: add wasm_import_module attribute for raw methods and improve content-type handling

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>

plugins/cmd/ndpgen/internal/parser.go

@@ -761,6 +761,7 @@ func parseMethod(name string, funcType *ast.FuncType, annotation map[string]stri
 	m := Method{
 		Name:       name,
 		ExportName: annotation["name"],
+		Raw:        annotation["raw"] == "true",
 		Doc:        doc,
 	}
 
@@ -799,6 +800,13 @@ func parseMethod(name string, funcType *ast.FuncType, annotation map[string]stri
 		}
 	}
 
+	// Validate raw=true methods: must return exactly (string, []byte, error)
+	if m.Raw {
+		if !m.HasError || len(m.Returns) != 2 || m.Returns[0].Type != "string" || m.Returns[1].Type != "[]byte" {
+			return m, fmt.Errorf("raw=true method %s must return (string, []byte, error) — content-type, data, error", name)
+		}
+	}
+
 	return m, nil
 }