feat: move OS.clock to IO.clock and remove deprecated os_clock native

Migrate the clock timing functionality from the OS class to the IO class across all benchmark scripts and the core library. Remove the os_clock native function and its associated OS class definition from wren_core.c, while adding a new ioClock native in wren_io.c that uses the same clock()/CLOCKS_PER_SEC logic. Update all benchmark files (binary_trees, fib, for, method_call) to reference IO.clock instead of OS.clock for both start time and elapsed time calculations.

benchmark/for.wren

@@ -1,10 +1,10 @@
 var list = []
 
-var start = OS.clock
+var start = IO.clock
 for (i in 0...1000000) list.add(i)
 
 var sum = 0
 for (i in list) sum = sum + i
 
 IO.print(sum)
-IO.print("elapsed: " + (OS.clock - start).toString)
+IO.print("elapsed: " + (IO.clock - start).toString)