fix(stdlib): Iterator::collect uses [] not nonexistent Vec (#135 slice 4-traits) (#169)

traits.affine:124 was the last parse blocker. Root cause is NOT a
compiler grammar gap: `while let` already parses. It is broken stdlib
code — `Iterator::collect` returned `Vec[Item]` and used `Vec::new()` /
`.push()`, but **`Vec` is not defined anywhere in the stdlib** (the
whole stdlib builds lists with `[]` + `++`, never `Vec`; `Vec::new()`
also exercised an unsupported `Type::lower_fn()` associated-call form).

Resolve-at-source: rewrite `collect` in the stdlib's own list idiom
(`let mut result = []; while let Some(item) = self.next() { result =
result ++ [item]; } return result`) rather than add speculative `Vec`
+ associated-function grammar to prop up code that never had a `Vec`.

Effect: traits.affine clears its last parse wall (PARSE 124 ->
TYPECHECK; the remaining `ref 't ~ Int` is a distinct deeper defect in
the `impl Eq for Int` blocks). Pure stdlib change — suite unaffected.

Advances #135. Refs #128, #135.

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

Author: hyperpolymath

stdlib/traits.affine

@@ -119,11 +119,13 @@ pub trait Iterator {
     return n;
   }
 
-  /// Collect into Vec
-  pub fn collect(mut self) -> Vec[Item] {
-    let mut result = Vec::new();
+  /// Collect into a list.  (`Vec` is not a stdlib type; the stdlib
+  /// builds lists with `[]` + `++`, as in prelude/option/result —
+  /// #135 slice 4-traits.)
+  pub fn collect(mut self) -> [Item] {
+    let mut result = [];
     while let Some(item) = self.next() {
-      result.push(item);
+      result = result ++ [item];
     }
     return result;
   }