fix(stdlib): builtins.map multi-iterable overloads use System.Func

The 2- and 3-iterable overloads typed the function as `'T1 * 'T2 -> 'T3`
(tuple-input), which Fable compiles to a Python function expecting a
single tuple arg. But Python's `map(f, it1, it2)` calls `f(a, b)`
positionally, so calls failed with "takes 1 positional argument but 2
were given". Switching to `System.Func<...>` produces a Python function
with the correct positional arity. Restores the two-iterable test and
adds a three-iterable test.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dbrattli

src/stdlib/Builtins.fs

@@ -186,11 +186,12 @@ type IExports =
 
     /// Make an iterator that computes the function using arguments from each
     /// of the iterables.  Stops when the shortest iterable is exhausted.
-    abstract map: ('T1 * 'T2 -> 'T3) * IEnumerable<'T1> * IEnumerable<'T2> -> IEnumerable<'T3>
+    abstract map: System.Func<'T1, 'T2, 'T3> * IEnumerable<'T1> * IEnumerable<'T2> -> IEnumerable<'T3>
 
     /// Make an iterator that computes the function using arguments from each
     /// of the iterables.  Stops when the shortest iterable is exhausted.
-    abstract map: ('T1 * 'T2 * 'T3 -> 'T4) * IEnumerable<'T1> * IEnumerable<'T2> * IEnumerable<'T3> -> IEnumerable<'T4>
+    abstract map:
+        System.Func<'T1, 'T2, 'T3, 'T4> * IEnumerable<'T1> * IEnumerable<'T2> * IEnumerable<'T3> -> IEnumerable<'T4>
 
     /// Return the Unicode code point for a one-character string.
     abstract ord: char -> int

test/TestBuiltins.fs

@@ -162,6 +162,18 @@ let ``test map with single iterable works`` () =
     |> Seq.toList
     |> equal [ 2; 4; 6 ]
 
+[<Fact>]
+let ``test map with two iterables works`` () =
+    builtins.map ((fun a b -> a + b), [ 1; 2; 3 ], [ 10; 20; 30 ])
+    |> Seq.toList
+    |> equal [ 11; 22; 33 ]
+
+[<Fact>]
+let ``test map with three iterables works`` () =
+    builtins.map ((fun a b c -> a + b + c), [ 1; 2; 3 ], [ 10; 20; 30 ], [ 100; 200; 300 ])
+    |> Seq.toList
+    |> equal [ 111; 222; 333 ]
+
 [<Fact>]
 let ``test str conversion works`` () =
     builtins.str 42 |> equal "42"