feat: replace eager map/where with lazy MapSequence and WhereSequence classes

Refactor Sequence.map and Sequence.where to return lazy MapSequence and WhereSequence wrappers instead of eagerly building a List. Add new MapSequence and WhereSequence classes that delegate iteration and apply the transformation or predicate on-the-fly. Update documentation to reflect lazy semantics and the need to call .list to materialize results. Adjust all existing tests to call .list on map/where results. Add new tests in test/core/sequence/ verifying lazy behavior with infinite Fibonacci iterators.

src/vm/wren_core.c

@@ -92,21 +92,9 @@ static const char* libSource =
 "    }\n"
 "  }\n"
 "\n"
-"  map(f) {\n"
-"    var result = new List\n"
-"    for (element in this) {\n"
-"      result.add(f.call(element))\n"
-"    }\n"
-"    return result\n"
-"  }\n"
+"  map(transformation) { new MapSequence(this, transformation) }\n"
 "\n"
-"  where(f) {\n"
-"    var result = new List\n"
-"    for (element in this) {\n"
-"      if (f.call(element)) result.add(element)\n"
-"    }\n"
-"    return result\n"
-"  }\n"
+"  where(predicate) { new WhereSequence(this, predicate) }\n"
 "\n"
 "  reduce(acc, f) {\n"
 "    for (element in this) {\n"
@@ -152,6 +140,32 @@ static const char* libSource =
 "  }\n"
 "}\n"
 "\n"
+"class MapSequence is Sequence {\n"
+"  new(seq, f) {\n"
+"    _seq = seq\n"
+"    _f = f\n"
+"  }\n"
+"\n"
+"  iterate(n) { _seq.iterate(n) }\n"
+"  iteratorValue(iterator) { _f.call(_seq.iteratorValue(iterator)) }\n"
+"}\n"
+"\n"
+"class WhereSequence is Sequence {\n"
+"  new(seq, f) {\n"
+"    _seq = seq\n"
+"    _f = f\n"
+"  }\n"
+"\n"
+"  iterate(n) {\n"
+"    while (n = _seq.iterate(n)) {\n"
+"      if (_f.call(_seq.iteratorValue(n))) break\n"
+"    }\n"
+"    return n\n"
+"  }\n"
+"\n"
+"  iteratorValue(iterator) { _seq.iteratorValue(iterator) }\n"
+"}\n"
+"\n"
 "class String is Sequence {\n"
 "  bytes { new StringByteSequence(this) }\n"
 "}\n"