stream: validate all elements in isUint8ArrayBatch

`isUint8ArrayBatch` only checked the first array element, so a
mixed array like `[Uint8Array, "hello"]` would pass the fast-path
check and flow through un-normalized.

Use `ArrayPrototypeEvery` to validate all elements. Also replaced
inline first-element-only checks in `processTransformResultSync`
and `processTransformResultAsync` with the corrected
`isUint8ArrayBatch` function.

Author: jasnell

lib/internal/streams/iter/from.js

@@ -253,8 +253,7 @@ function* normalizeSyncValue(value) {
 function isUint8ArrayBatch(value) {
   if (!ArrayIsArray(value)) return false;
   if (value.length === 0) return true;
-  // Check first element - if it's a Uint8Array, assume the rest are too
-  return isUint8Array(value[0]);
+  return ArrayPrototypeEvery(value, isUint8Array);
 }
 
 /**

lib/internal/streams/iter/pull.js

@@ -7,7 +7,6 @@
 // through transforms to consumer.
 
 const {
-  ArrayIsArray,
   ArrayPrototypePush,
   ArrayPrototypeSlice,
   String,
@@ -178,9 +177,7 @@ function* processTransformResultSync(result) {
   if (result === null) {
     return;
   }
-  if (ArrayIsArray(result) && result.length > 0 &&
-      isUint8Array(result[0])) {
-    // Fast path: Uint8Array[]
+  if (isUint8ArrayBatch(result)) {
     if (result.length > 0) {
       yield result;
     }
@@ -216,9 +213,7 @@ async function* processTransformResultAsync(result) {
   if (result === null) {
     return;
   }
-  if (ArrayIsArray(result) &&
-      (result.length === 0 || isUint8Array(result[0]))) {
-    // Fast path: Uint8Array[]
+  if (isUint8ArrayBatch(result)) {
     if (result.length > 0) {
       yield result;
     }