test: add tests for lambda leak cases

Adds tests to ensure lambdas do not leak ownership of their captured
variables. In addition, the nested lambda test now needs to accept a
reference to a function instead of a function value (otherwise an
ownership leak occurs).

examples/nested_lambdas.carp

@@ -1,5 +1,5 @@
-(defn my-curry [f] (fn [x] (fn [y] (f x y))))
-(defn double-curry [f] (fn [x] (fn [y] (fn [z] (f x y z)))))
+(defn my-curry [f] (fn [x] (fn [y] (~f x y))))
+(defn double-curry [f] (fn [x] (fn [y] (fn [z] (~f x y z)))))
 
 (defn make-cb []
   ((fn []
@@ -15,4 +15,4 @@
 (defn main []
   (do ((make-cb))
       ((make-cb2))
-      (((my-curry (fn [x y] (Int.+ x y))) 1) 2)))
+      (((my-curry &(fn [x y] (Int.+ x y))) 1) 2)))

test/output/test/test-for-errors/lambda_leaking_capture_ownership.carp.output.expected

@@ -0,0 +1,2 @@
+lambda_leaking_capture_ownership.carp:4:2 [ERROR] `I expected an array of valid arguments, but got: (let [string (copy "") leaks (fn [] s)])
+  - `defn` requires an array of arugments, but it got: (let [string (copy "") leaks (fn [] s)])

test/test-for-errors/lambda_leaking_capture_ownership.carp

@@ -0,0 +1,7 @@
+(Project.config "file-path-print-length" "short")
+
+;; see [issue #1040](https://github.com/carp-lang/Carp/issues/1040)
+(defn lambda-leak
+  (let [string @""
+        leaks (fn [] s)]) ;; disallow this
+  ())