feat: add onFetchError prop

[siddydutta]

Fixes #266.

Usage:

function App() {
  const handleOnFetchError = (error) => {
    console.error("Fetch error:", error);
    // Add any custom error handling here
  };

  return (
    <div className="App">
      <DocViewer
        documents={{ uri: "https://example.com/sample.pdf" }}
        onFetchError={handleOnFetchError}
      />
    </div>
  );
}

[that-one-arab]

+1 to get this merged

[yt94kd]

We use this plugin for medical purposes, so I will be very glad if you will approve this very useful feature:)