lib: optimize writable stream buffer clearing

Improved the `clearBuffer` function
by replacing `buffered.splice` with `ArrayPrototypeSlice`.
- Eliminates O(N) shifting overhead.
- Improves CPU utilization and reduces GC overhead.

Author: ri7116

lib/internal/streams/writable.js

@@ -784,7 +784,7 @@ function clearBuffer(stream, state) {
     if (i === buffered.length) {
       resetBuffer(state);
     } else if (i > 256) {
-      buffered.splice(0, i);
+      state[kBufferedValue] = ArrayPrototypeSlice(buffered, i);
       state.bufferedIndex = 0;
     } else {
       state.bufferedIndex = i;