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.

test/core/list/map.wren

@@ -1,3 +1,3 @@
 var a = [1, 2, 3]
-var b = a.map {|x| x + 1 }
+var b = a.map {|x| x + 1 }.list
 IO.print(b) // expect: [2, 3, 4]

test/core/list/where.wren

@@ -1,6 +1,6 @@
 var a = [1, 2, 3]
-var b = a.where {|x| x > 1 }
+var b = a.where {|x| x > 1 }.list
 IO.print(b) // expect: [2, 3]
 
-var c = a.where {|x| x > 10 }
+var c = a.where {|x| x > 10 }.list
 IO.print(c) // expect: []