feat(discovery): add discover_devices_stream streaming variant

[Irishsmurf]

Closes #33

[gemini-code-assist]

Code Review

This pull request introduces discover_devices_stream, an asynchronous generator that yields discovered dLight devices incrementally as they respond. It also updates the documentation and adds unit tests for this new feature. The reviewer feedback highlights a potential data loss issue in the streaming loop if consumer processing delays cause a timeout, suggesting yielding all buffered devices before exiting. Additionally, the reviewer suggests making the results_list parameter optional in _DiscoveryProtocol to avoid unnecessary list allocations during streaming discovery.

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