function base64ToUint8Array(base64String) {
  try {
    const binaryString = atob(base64String);
    const len = binaryString.length;
    const bytes = new Uint8Array(len);
    for (let i = 0; i < len; i++) bytes[i] = binaryString.charCodeAt(i);
    return bytes;
  } catch (e) {
    console.error(
      `[AWSBedrock] Error decoding base64 string with atob: ${e.message}`
    );
    return null;
  }
}
Decodes a pure base64 string (without data URI prefix) into a Uint8Array using the atob method.
This approach matches the technique previously used by Langchain's implementation.
@param {string} base64String - The pure base64 encoded data.
@returns {Uint8Array | null} The resulting byte array or null on decoding error.