fix: metrics of strings in RimeProto were not completely converted

app/src/main/java/com/osfans/trime/core/RimeProto.kt

@@ -19,16 +19,29 @@ class RimeProto {
         val composition: Composition,
         val menu: Menu,
         val input: String,
-        val caretPos: Int,
+        private val _caretPos: Int,
     ) {
+        /**
+         * Same with [Composition.cursorPos], just directly assign to it.
+         */
+        val caretPos = composition.cursorPos
+
         data class Composition(
-            val length: Int = 0,
-            val cursorPos: Int = 0,
+            private val _length: Int = 0,
+            private val _cursorPos: Int = 0,
             private val _selStart: Int = 0,
             private val _selEnd: Int = 0,
             val preedit: String? = null,
             val commitTextPreview: String? = null,
         ) {
+            /**
+             * Actually we can directly use [String.length] on [preedit], but
+             * we add it here for the sake of completeness as it is semantically correct
+             */
+            val length: Int = preedit.run { if (isNullOrEmpty()) 0 else String(toByteArray(), 0, _length).length }
+
+            val cursorPos: Int = preedit.run { if (isNullOrEmpty()) 0 else String(toByteArray(), 0, _cursorPos).length }
+
             val selStart: Int = preedit.run { if (isNullOrEmpty()) 0 else String(toByteArray(), 0, _selStart).length }
 
             val selEnd: Int = preedit.run { if (isNullOrEmpty()) 0 else String(toByteArray(), 0, _selEnd).length }