Improve handling of evaluator in multi-file output (#1670)

* Re-use same evaluator across output dirs
* Close evaluator after all files are written

pkl-cli/src/main/kotlin/org/pkl/cli/CliEvaluator.kt

@@ -229,8 +229,8 @@ constructor(
   private fun writeMultipleFileOutput(builder: EvaluatorBuilder) {
     val outputDirs = directoryOutputPaths!!
     val writtenFiles = mutableMapOf<Path, OutputFile>()
+    builder.setOutputFormat(options.outputFormat).build().use { evaluator ->
       for ((moduleUri, outputDir) in outputDirs) {
-      val evaluator = builder.setOutputFormat(options.outputFormat).build()
         if (outputDir.exists() && !outputDir.isDirectory()) {
           throw CliException("Output path `$outputDir` exists and is not a directory.")
         }
@@ -268,6 +268,7 @@ constructor(
         }
       }
     }
+  }
 
   /**
    * Resolves [rel] against this Path name-by-name. At each step, the real path is resolved if the