Replace CSVWriter with manual string building for KMP migration

uhabits-core/src/commonMain/kotlin/org/isoron/platform/io/Strings.kt

@@ -22,3 +22,13 @@ package org.isoron.platform.io
 expect fun format(format: String, arg: String): String
 expect fun format(format: String, arg: Int): String
 expect fun format(format: String, arg: Double): String
+
+fun csvLine(fields: Array<String>): String {
+    return fields.joinToString(",") { field ->
+        if (field.any { it == ',' || it == '"' || it == '\n' || it == '\r' }) {
+            "\"${field.replace("\"", "\"\"")}\""
+        } else {
+            field
+        }
+    } + "\n"
+}

uhabits-core/src/jvmMain/java/org/isoron/uhabits/core/models/HabitList.kt

@@ -18,7 +18,7 @@
  */
 package org.isoron.uhabits.core.models
 
-import com.opencsv.CSVWriter
+import org.isoron.platform.io.csvLine
 import org.isoron.platform.io.format
 import java.io.IOException
 import java.io.Writer
@@ -192,8 +192,7 @@ abstract class HabitList : Iterable<Habit> {
             "Target Value",
             "Archived?"
         )
-        val csv = CSVWriter(out)
-        csv.writeNext(header, false)
+        out.write(csvLine(header))
         for (habit in this) {
             val (numerator, denominator) = habit.frequency
             val cols = arrayOf(
@@ -210,9 +209,9 @@ abstract class HabitList : Iterable<Habit> {
                 if (habit.isNumerical) habit.targetValue.toString() else "",
                 habit.isArchived.toString()
             )
-            csv.writeNext(cols, false)
+            out.write(csvLine(cols))
         }
-        csv.close()
+        out.close()
     }
 
     abstract fun resort()