Add option to get screenshot as a buffer

[Christian-Holbrook]

Adds returnBuffer option to captureScreenshot() that returns a Buffer instead of writing to disk.

Closes #172

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API

  // Existing behavior - returns file path
  const path = await rokuDeploy.captureScreenshot({ host, password });


  // New behavior - returns Buffer
  const buffer = await rokuDeploy.captureScreenshot({ host, password, returnBuffer: true });

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Why Overloads?

TypeScript overloads provide proper return type inference based on the options passed:

// TypeScript knows this is Promise<Buffer>
const buffer = await captureScreenshot({ host, password, returnBuffer: true });

// TypeScript knows this is Promise<string>
const path = await captureScreenshot({ host, password });

Without overloads, the return type would be Promise<string | Buffer>, requiring users to narrow the type manually:

  // Without overloads - awkward
  const result = await captureScreenshot({ host, password, returnBuffer: true });
  if (Buffer.isBuffer(result)) {
    // now we can use it as Buffer
  }

This pattern follows the existing convention in the codebase (see getDeviceInfo() with its enhance option).