update ValueStreamBuilder

[hoc081098]

This pull request includes several changes to the ValueStreamBuilder class in the packages/rxdart_flutter library. The changes focus on improving error handling, updating documentation, and enhancing the overall robustness of the ValueStreamBuilder class.

Improvements to error handling:

• packages/rxdart_flutter/lib/src/value_stream_builder.dart: Replaced the Object? error field with ErrorAndStackTrace? error to better capture error details.
• packages/rxdart_flutter/lib/src/value_stream_builder.dart: Updated the error handling logic to use the new ErrorAndStackTrace class and introduced a new reportError method for reporting errors consistently. [1] [2]

Documentation updates:

• packages/rxdart_flutter/lib/src/value_stream_builder.dart: Enhanced the documentation for ValueStreamBuilder to clarify its requirements and added examples. [1] [2]

Robustness improvements:

• packages/rxdart_flutter/lib/src/value_stream_builder.dart: Updated the build method to return an ErrorWidget instead of throwing an error directly when an error occurs.
• packages/rxdart_flutter/lib/src/value_stream_builder.dart: Improved the error messages in UnhandledStreamError and ValueStreamHasNoValueError classes to provide clearer guidance and formatting.