feat: migrate all function literals from fn syntax to new Fn block syntax

Replace all occurrences of the old `fn` function literal syntax with the new `new Fn {|params| body}` block syntax across benchmark, test, and source files. Update the Wren compiler to handle the pipe operator as a block argument delimiter by removing `TOKEN_PIPE` from the newline-swallowing token list and adding explicit newline matching in `infixOp`. Adjust test expectations in `conditional/precedence.wren` to remove `fn`-based expressions and update `test/assignment/local.wren` to use the new syntax.

script/test.py

@@ -180,8 +180,9 @@ def run_test(path):
 
   # Validate the exit code.
   if proc.returncode != expect_return:
-    fails.append('Expected return code {0} and got {1}.'
+    fails.append('Expected return code {0} and got {1}. Stderr:'
         .format(expect_return, proc.returncode))
+    fails += err.split('\n')
   else:
     # Validate the output.
     expect_index = 0