added label syntax support and highlighting

lynglib/src/commonTest/kotlin/net/sergeych/lyng/format/LyngFormatterTest.kt

@@ -21,6 +21,15 @@ import kotlin.test.assertEquals
 
 class LyngFormatterTest {
 
+    @Test
+    fun labelFormatting() {
+        val src = "return  @label; break  @outer; continue  @inner"
+        val expected = "return@label; break@outer; continue@inner"
+        val cfg = LyngFormatConfig(applySpacing = true)
+        val out = LyngFormatter.format(src, cfg)
+        assertEquals(expected, out)
+    }
+
     @Test
     fun reindent_simpleFunction() {
         val src = """

lynglib/src/commonTest/kotlin/net/sergeych/lyng/highlight/HighlightMappingTest.kt

@@ -25,6 +25,16 @@ class HighlightMappingTest {
     private fun spansToLabeled(text: String, spans: List<HighlightSpan>): List<Pair<String, HighlightKind>> =
         spans.map { text.substring(it.range.start, it.range.endExclusive) to it.kind }
 
+    @Test
+    fun returnAndExits() {
+        val text = "return 42; break@outer null"
+        val spans = SimpleLyngHighlighter().highlight(text)
+        val labeled = spansToLabeled(text, spans)
+        assertTrue(labeled.any { it.first == "return" && it.second == HighlightKind.Keyword })
+        assertTrue(labeled.any { it.first == "break" && it.second == HighlightKind.Keyword })
+        assertTrue(labeled.any { it.first == "@outer" && it.second == HighlightKind.Label })
+    }
+
     @Test
     fun keywordsAndIdentifiers() {
         val text = "a and b or not c"