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/list/map.wren

@@ -1,3 +1,3 @@
 var a = [1, 2, 3]
-var b = a.map(fn (x) x + 1)
+var b = a.map {|x| x + 1 }
 IO.print(b) // expect: [2, 3, 4]

test/list/where.wren

@@ -1,6 +1,6 @@
 var a = [1, 2, 3]
-var b = a.where(fn (x) x > 1)
+var b = a.where {|x| x > 1 }
 IO.print(b) // expect: [2, 3]
 
-var c = a.where(fn (x) x > 10)
+var c = a.where {|x| x > 10 }
 IO.print(c) // expect: []