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.

test/variable/local_collide_with_function_parameter.wren

@@ -1,3 +1,3 @@
-fn(a) {
+new Fn {|a|
   var a = "oops" // expect error
 }

test/variable/undefined_local.wren

@@ -1,3 +1,3 @@
-fn {
+new Fn {
   IO.print(notDefined)  // expect error
 }.call