feat: move contains method from List to Sequence and add tests for List and Range

Add a generic `contains` implementation on the `Sequence` base class, removing the duplicate method from `List`. This allows all sequence types (including Range) to use the method without per-class redefinition. Include new test files for `List.contains` and `Range.contains` covering ordered, backwards, and exclusive ranges.

src/vm/wren_core.c

@@ -45,6 +45,15 @@
 // This string literal is generated automatically from core. Do not edit.
 static const char* libSource =
 "class Sequence {\n"
+"  contains(element) {\n"
+"    for (item in this) {\n"
+"      if (element == item) {\n"
+"        return true\n"
+"      }\n"
+"    }\n"
+"    return false\n"
+"  }\n"
+"\n"
 "  count {\n"
 "    var result = 0\n"
 "    for (element in this) {\n"
@@ -138,15 +147,6 @@ static const char* libSource =
 "    }\n"
 "    return result\n"
 "  }\n"
-"\n"
-"  contains(element) {\n"
-"    for (item in this) {\n"
-"      if (element == item) {\n"
-"        return true\n"
-"      }\n"
-"    }\n"
-"    return false\n"
-"  }\n"
 "}\n"
 "\n"
 "class Map {\n"