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/limit/long_function.wren

@@ -1,4 +1,4 @@
-fn {
+new Fn {
   IO.print(1) // expect: 1
   IO.print(2) // expect: 2
   IO.print(3) // expect: 3

test/limit/many_constants.wren

@@ -1,4 +1,4 @@
-var f = fn {
+var f = new Fn {
   1; 2; 3; 4; 5; 6; 7; 8;
   9; 10; 11; 12; 13; 14; 15; 16;
   17; 18; 19; 20; 21; 22; 23; 24;