chore: Make Settings a case class (#490)

Motivation:
Making it a case class then I can do `Settings.default.copy(...)`

Author: He-Pin

build.mill

@@ -317,7 +317,7 @@ object sjsonnet extends VersionFileModule {
       "--initialize-at-build-time",
       "--initialize-at-run-time=os.package$",
       "--install-exit-handlers",
-      "-H:+ReportExceptionStackTraces",
+      "-H:+ReportExceptionStackTraces"
     )
   }
 }

sjsonnet/src/sjsonnet/Settings.scala

@@ -4,7 +4,7 @@ package sjsonnet
  * Settings for the interpreter. This is a subset of Config which is used in the inner layers of the
  * interpreters and shared between all platforms.
  */
-class Settings(
+case class Settings(
     val preserveOrder: Boolean = false,
     val strict: Boolean = false,
     val throwErrorForInvalidSets: Boolean = false,