feat!: rework the public API to json/v2-style variadic options

Assisted-by: GLM 5.3 Flash

encode.go

@@ -111,12 +111,22 @@ func getEncoderBuf() *bytes.Buffer {
 	return b
 }
 
+// encodeConfig carries the public emission options one Marshal call applies;
+// the names and defaults are documented on the MarshalOption constructors.
+type encodeConfig struct {
+	layout             LayoutKind
+	omitEmptyArrays    bool
+	literalMultilineAt int
+	inlineTablesAt     int
+	emitFieldComments  bool
+}
+
 // encoder produces a TOML document from a Go value via a small intermediate
 // representation that preserves the order in which fields were declared.
 type encoder struct {
 	buf  *bytes.Buffer
 	ctx  context.Context
-	opts Encoder
+	opts encodeConfig
 
 	// inlineDepth is the nesting level inside inline tables, which decides
 	// their indentation.
@@ -329,7 +339,7 @@ type entry struct {
 type tomlDoc struct {
 	entries []entry
 	ctx     context.Context // inherited from encoder; nil-safe
-	opts    Encoder         // inherited from encoder; options drive emit-time behaviour
+	opts    encodeConfig    // inherited from encoder; options drive emit-time behaviour
 	depth   int
 }