Fix cache files being padded with trailing 0's

buffer() was offseting the array instead of truncating the returned
array.

src/webgpu/shader/execution/expression/case_cache.ts

@@ -166,13 +166,13 @@ export class CaseCache implements Cacheable<Record<string, CaseList>> {
    */
   serialize(data: Record<string, CaseList>): Uint8Array {
     const maxSize = 32 << 20; // 32MB - max size for a file
-    const s = new BinaryStream(new Uint8Array(maxSize).buffer);
-    s.writeU32(Object.keys(data).length);
+    const stream = new BinaryStream(new ArrayBuffer(maxSize));
+    stream.writeU32(Object.keys(data).length);
     for (const name in data) {
-      s.writeString(name);
-      s.writeArray(data[name], serializeCase);
+      stream.writeString(name);
+      stream.writeArray(data[name], serializeCase);
     }
-    return new Uint8Array(s.buffer());
+    return stream.buffer();
   }
 
   /**

src/webgpu/util/binary_stream.ts

@@ -19,8 +19,8 @@ export default class BinaryStream {
   }
 
   /** buffer() returns the stream's buffer sliced to the 8-byte rounded read or write offset */
-  buffer(): ArrayBufferLike {
-    return new Uint8Array(this.view.buffer, align(this.offset, 8)).buffer;
+  buffer(): Uint8Array {
+    return new Uint8Array(this.view.buffer, 0, align(this.offset, 8));
   }
 
   /** writeBool() writes a boolean as 255 or 0 to the buffer at the next byte offset */