fix: replace hashBits with V8's integer hash to fix catastrophic collision for numeric keys

The old hashBits function XORed the two 32-bit halves of a double and applied
Java HashMap-style mixing, but for small integers the low bits of the double
representation are mostly zero, causing nearly all keys to map to entry zero.
This replaces it with Thomas Wang's integer hash (as used by V8's
ComputeLongHash), which properly scatters bits across the 32-bit key space.
Also updates the map_numeric benchmark to iterate 2,000,000 entries (up from
1,000,000) and adjusts the expected output in util/benchmark.py accordingly.

test/benchmark/map_numeric.dart.skip

@@ -6,17 +6,17 @@ main() {
 
   var map = {};
 
-  for (var i = 1; i <= 1000000; i++) {
+  for (var i = 1; i <= 2000000; i++) {
     map[i] = i;
   }
 
   var sum = 0;
-  for (var i = 1; i <= 1000000; i++) {
+  for (var i = 1; i <= 2000000; i++) {
     sum += map[i];
   }
   print(sum);
 
-  for (var i = 1; i <= 1000000; i++) {
+  for (var i = 1; i <= 2000000; i++) {
     map.remove(i);
   }
 

test/benchmark/map_numeric.lua

@@ -2,17 +2,17 @@ local start = os.clock()
 
 local map = {}
 
-for i = 1, 1000000 do
+for i = 1, 2000000 do
   map[i] = i
 end
 
 local sum = 0
-for i = 1, 1000000 do
+for i = 1, 2000000 do
   sum = sum + map[i]
 end
 io.write(string.format("%d\n", sum))
 
-for i = 1, 1000000 do
+for i = 1, 2000000 do
   map[i] = nil
 end
 

test/benchmark/map_numeric.py

@@ -6,15 +6,15 @@ start = time.clock()
 
 map = {}
 
-for i in range(1, 1000001):
+for i in range(1, 2000001):
   map[i] = i
 
 sum = 0
-for i in range(1, 1000001):
+for i in range(1, 2000001):
   sum = sum + map[i]
 print(sum)
 
-for i in range(1, 1000001):
+for i in range(1, 2000001):
   del map[i]
 
 print("elapsed: " + str(time.clock() - start))

test/benchmark/map_numeric.rb

@@ -2,17 +2,17 @@ start = Time.now
 
 map = Hash.new
 
-for i in (1..1000000)
+for i in (1..2000000)
   map[i] = i
 end
 
 sum = 0
-for i in (1..1000000)
+for i in (1..2000000)
   sum = sum + map[i]
 end
 puts sum
 
-for i in (1..1000000)
+for i in (1..2000000)
   map.delete(i)
 end
 

test/benchmark/map_numeric.wren

@@ -2,17 +2,17 @@ var start = System.clock
 
 var map = {}
 
-for (i in 1..1000000) {
+for (i in 1..2000000) {
   map[i] = i
 }
 
 var sum = 0
-for (i in 1..1000000) {
+for (i in 1..2000000) {
   sum = sum + map[i]
 }
 System.print(sum)
 
-for (i in 1..1000000) {
+for (i in 1..2000000) {
   map.remove(i)
 }