Binary ArrayBufferView slices send the entire backing buffer #202

Description

Binary requests made with a sliced ArrayBufferView send the view's entire backing buffer instead of only the selected byte range.

methodRequest() converts non-DataView views with new DataView(opts.body.buffer) at src/core.ts:276. That drops the original view's byteOffset and byteLength. RequestOptions explicitly accepts ArrayBufferView, so callers can reasonably pass Buffer.subarray(), Uint8Array.subarray(), or another bounded view.

Reproduction

import Browserbase from '@browserbasehq/sdk';

let sentBody: any;
const client = new Browserbase({
  apiKey: 'test',
  maxRetries: 0,
  fetch: async (_url, init) => {
    sentBody = init?.body;
    return new Response('{}', {
      status: 200,
      headers: { 'content-type': 'application/json' },
    });
  },
});

const backing = new Uint8Array([10, 20, 30, 40]);
await client.post('/binary', {
  body: backing.subarray(1, 3),
  __binaryRequest: true,
});

console.log(sentBody.byteLength); // 4, expected 2
console.log([...new Uint8Array(sentBody.buffer)]); // [10, 20, 30, 40]

Expected behavior

Only the selected bytes ([20, 30]) are sent, and the request body/content length is 2 bytes.

Actual behavior

All four bytes in the backing buffer are sent.

Why this matters

This corrupts binary payloads and can disclose adjacent bytes that the caller deliberately excluded with a view. The conversion should preserve byteOffset and byteLength, for example with new DataView(view.buffer, view.byteOffset, view.byteLength), and have regression coverage for sliced Uint8Array/Buffer values.

Tested against @browserbasehq/sdk 2.18.0 / current main (b781bd7).