feat(realtime): add support for target streaming delay in realtime transcription

This commit introduces the ability to specify a target streaming delay in milliseconds for realtime transcription sessions. The changes include:

1. Adding a new parameter `target_streaming_delay_ms` to the realtime transcription API
2. Updating the connection management to handle the new delay parameter
3. Adding support for audio flushing to ensure proper handling of streaming delays
4. Creating a new example demonstrating dual-delay transcription with two parallel streams
5. Improving error handling for microphone access and PyAudio loading

The changes allow for more precise control over the latency/accuracy tradeoff in realtime transcription, enabling use cases that require different streaming delays for different purposes.

Author: jean-malo