refactor: rename the encoder layout options

Assisted-by: GLM 5.3 Flash

encode.go

@@ -295,7 +295,7 @@ const (
 
 // entry is one binding in a tomlDoc. entries live in a single slice in the
 // order they were added; emission walks that order directly, either as it is
-// (Encoder with GroupByKind(false)) or in kind-grouped passes over the same
+// (Encoder with LayoutKindDeclaration) or in kind-grouped passes over the same
 // slice (the default).
 type entry struct {
 	kind entryKind
@@ -1157,7 +1157,7 @@ func (e *encoder) writeBlankLine() {
 }
 
 func (e *encoder) emitDoc(doc *tomlDoc, prefix []string) error {
-	if e.opts.groupByKind {
+	if e.opts.layout == LayoutKindGrouped {
 		// Scalars first, then inline sub-tables as value lines, then the
 		// remaining tables as headers, then arrays of tables. Each pass walks
 		// the entries in place; grouping copies of them cost the encoder a