Fix useBuffer() targetView assignment

[iamarkdev]

The useBuffer() method was not properly initializing the module-level targetView variable, causing TypeError: undefined is not an object (evaluating 'targetView.setFloat64') and similar errors when packing data that requires DataView operations.

Root Cause

When useBuffer(buffer) is called, it correctly sets:

• ✅ target = buffer
• ✅ position = 0
• ❌ targetView remains undefined
  Later, when pack() executes, it checks if (!target) to decide whether to initialize. Since target is already set by useBuffer(), the initialization block that sets targetView = target.dataView is skipped, leaving targetView undefined.

Fix

Added targetView = target.dataView to useBuffer() to ensure both target and targetView are properly initialized when using external buffers.

This enables proper buffer reuse patterns and prevents runtime errors when packing numbers, which require DataView methods like setFloat64(), setUint32(), etc.