[perf] Reduce the amount of crypto.randomFillSync() calls

Use a pool of random bytes to reduce the amount of
`crypto.randomFillSync()` calls.

Refs: nodejs/undici#3204

lib/sender.js

@@ -12,6 +12,9 @@ const { mask: applyMask, toBuffer } = require('./buffer-util');
 
 const kByteLength = Symbol('kByteLength');
 const maskBuffer = Buffer.alloc(4);
+const RANDOM_POOL_SIZE = 8 * 1024;
+let randomPool;
+let randomPoolPointer = RANDOM_POOL_SIZE;
 
 /**
  * HyBi Sender implementation.
@@ -76,7 +79,19 @@ class Sender {
       if (options.generateMask) {
         options.generateMask(mask);
       } else {
-        randomFillSync(mask, 0, 4);
+        if (randomPoolPointer === RANDOM_POOL_SIZE) {
+          if (randomPool === undefined) {
+            randomPool = Buffer.alloc(RANDOM_POOL_SIZE);
+          }
+
+          randomFillSync(randomPool, 0, RANDOM_POOL_SIZE);
+          randomPoolPointer = 0;
+        }
+
+        mask[0] = randomPool[randomPoolPointer++];
+        mask[1] = randomPool[randomPoolPointer++];
+        mask[2] = randomPool[randomPoolPointer++];
+        mask[3] = randomPool[randomPoolPointer++];
       }
 
       skipMasking = (mask[0] | mask[1] | mask[2] | mask[3]) === 0;