Fix response.body.getReader compatibility with node-fetch

[Copilot]

Issue

When using this library with node-fetch instead of native fetch, it would fail with an error: response.body.getReader is not a function. This is because node-fetch doesn't implement the Web Streams API in the same way as native fetch.

Solution

This PR adds support for both implementations:

1. It checks if response.body.getReader() is available (native fetch)
2. If available, it uses the existing implementation with getReader()
3. If not available, it falls back to a Node.js stream implementation using event listeners

The implementation maintains identical timeout and error handling behaviors between both approaches.

Changes

• Added a check for response.body.getReader availability
• Added a new processNodeStream function for node-fetch compatible streams
• Updated documentation to clarify compatibility with both fetch implementations
• Added a simple compatibility test

This change enables the library to work with both Node.js 18+ (with native fetch) and older Node.js versions using node-fetch as a fallback without any code changes required by the user.

Fixes #6.

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