feat: add benchmark runner with fib implementations and OS.clock primitive

Add a benchmark runner script (benchmark/run_all) that executes multiple
fibonacci implementations across languages (Lua, Python, Ruby, Wren) and
computes mean, median, and standard deviation from 7 runs. Update existing
fib benchmarks to loop 5 times at fib(30) with elapsed timing. Introduce
OS.clock primitive in C core and OS class to support timing in Wren.
Adjust number formatting to "%.14g" for consistent output precision.

src/primitives.c

@@ -2,6 +2,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 
 #include "compiler.h"
 #include "primitives.h"
@@ -93,7 +94,7 @@ DEF_PRIMITIVE(num_toString)
 {
   // TODO(bob): What size should this be?
   char temp[100];
-  sprintf(temp, "%g", AS_NUM(args[0]));
+  sprintf(temp, "%.14g", AS_NUM(args[0]));
   return (Value)newString(vm, temp, strlen(temp));
 }
 
@@ -235,6 +236,12 @@ DEF_PRIMITIVE(io_write)
   return args[1];
 }
 
+DEF_PRIMITIVE(os_clock)
+{
+  double time = (double)clock() / CLOCKS_PER_SEC;
+  return NUM_VAL(time);
+}
+
 static const char* CORE_LIB =
 "class Object {}\n"
 "class Bool {}\n"
@@ -244,7 +251,8 @@ static const char* CORE_LIB =
 "class Null {}\n"
 "class String {}\n"
 "class IO {}\n"
-"var io = IO.new\n";
+"var io = IO.new\n"
+"class OS {}\n";
 
 void loadCore(VM* vm)
 {
@@ -301,6 +309,9 @@ void loadCore(VM* vm)
   ObjClass* ioClass = AS_CLASS(findGlobal(vm, "IO"));
   PRIMITIVE(ioClass, "write ", io_write);
 
+  ObjClass* osClass = AS_CLASS(findGlobal(vm, "OS"));
+  PRIMITIVE(osClass->metaclass, "clock", os_clock);
+
   ObjClass* unsupportedClass = newClass(vm, vm->objectClass);
 
   // TODO(bob): Make this a distinct object type.

src/vm.c

@@ -1031,7 +1031,7 @@ void printValue(Value value)
 #ifdef NAN_TAGGING
   if (IS_NUM(value))
   {
-    printf("%g", AS_NUM(value));
+    printf("%.14g", AS_NUM(value));
   }
   else if (IS_OBJ(value))
   {
@@ -1059,7 +1059,7 @@ void printValue(Value value)
   {
     case VAL_FALSE: printf("false"); break;
     case VAL_NULL: printf("null"); break;
-    case VAL_NUM: printf("%g", AS_NUM(value)); break;
+    case VAL_NUM: printf("%.14g", AS_NUM(value)); break;
     case VAL_TRUE: printf("true"); break;
     case VAL_OBJ:
       switch (value.obj->type)